Skip to content
CalcTheJob

Methodology & Sources

First published · Last reviewed

This page collects, in one place, the method and the sources behind every CalcTheJob calculator. Each calculator page also shows its own Sources & assumptions section. CalcTheJob is an independent site; see About for who runs it.

General method

  • Geometry first. Areas and volumes come from standard formulas (length × width × depth, πr², roof slope factor √(1 + (rise ÷ 12)²)). 1 cubic yard = 27 cu ft; 1 short ton = 2,000 lb.
  • Published product data. Bag yields, coverage rates and packaging come from manufacturer data sheets, linked below. Where brands differ, we use a typical value and let you enter your own.
  • Codes and public guidance. Code limits (such as deck joist spacing) and public estimating figures (such as state DOT aggregate weights or extension-service mulch depths) are cited where we use them.
  • Rounding. Counts you buy — bags, boxes, sheets, bundles, rolls, loads — are always rounded up to whole units. Volumes and weights are shown to at most two decimals.
  • Waste. A visible, adjustable percentage (10% by default in most tools; pattern-based for tile) is applied to the whole job before rounding, not to each piece.
  • Testing. The calculation code has automated tests that check results against worked examples and reference values.

Calculator by calculator

Concrete Bag Calculator

  • Bag yields follow the manufacturer data sheet: 0.30, 0.375, 0.45 and 0.60 cu ft for 40, 50, 60 and 80 lb bags (45 × 80 lb bags per cubic yard).
  • The default 10% extra covers spillage, uneven subgrade and form bulge; change it in the tool.
  • Bag counts are always rounded up to whole bags.

Sources:

  1. QUIKRETE, Concrete Mix No. 1101 product data sheet. Bag yields: 40 lb ≈ 0.30 cu ft, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft.
  2. ASTM International, ASTM C387/C387M, Standard Specification for Packaged, Dry, Combined Materials for Concrete and High Strength Mortar. The product standard bagged concrete mixes are made to.

Concrete Calculator

  • Volumes use standard geometry for slabs, footings, round columns and steps; 27 cu ft = 1 cubic yard.
  • Bag counts use the manufacturer's published yields (80 lb ≈ 0.60 cu ft).
  • The default 10% extra is an ordering allowance, not a structural figure. Bags are rounded up to whole bags.

Sources:

  1. QUIKRETE, Concrete Mix No. 1101 product data sheet. Bag yields: 40 lb ≈ 0.30 cu ft, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft.
  2. ASTM International, ASTM C387/C387M, Standard Specification for Packaged, Dry, Combined Materials for Concrete and High Strength Mortar. The product standard bagged concrete mixes are made to.

Gravel Calculator

  • Tons = cubic yards × density. Default densities are loose, as-delivered planning figures of about 1.3–1.5 tons per cubic yard depending on material; your supplier's number is better, so the tool lets you change it.
  • Moisture and gradation move real weights by roughly 10–15%. Dense-graded base compacts, so add a compaction allowance when you are building a compacted base.
  • Bags (0.5 cu ft) and truck loads are rounded up.

Sources:

  1. Missouri Department of Transportation, Engineering Policy Guide 450, Estimate Factors (archived PDF). Gravel, crushed stone and chat estimated at 1.40 tons per cubic yard of loose aggregate.
  2. Two Rivers-Ottauquechee Regional Commission (Vermont), Material Weight: Pounds per Cubic Yard. Reference weights, e.g. crushed stone 2,700 lb/yd³, dry ¾ in gravel 2,565, pea gravel 2,700, dry sand 2,750.

French Drain Gravel Calculator

  • Stone volume = trench volume minus the space taken by the pipe, using the pipe's outside diameter.
  • Corrugated pipe outside diameters come from the maker's specification (about 4.6 in for 4 in pipe, 7.0 in for 6 in); 4 in PVC drain pipe is about 4.215 in OD.
  • Stone is converted to tons with a loose-aggregate density of about 1.4 tons per cubic yard unless you change it. Pipe sections, fabric and stone are rounded up.

Sources:

  1. Advanced Drainage Systems (ADS), ADS Single Wall Pipe Specification (Drainage Handbook). Reference pipe outside diameters: 4.6 in for 4 in, 7.0 in for 6 in.
  2. Missouri Department of Transportation, Engineering Policy Guide 450, Estimate Factors (archived PDF). Gravel, crushed stone and chat estimated at 1.40 tons per cubic yard of loose aggregate.

Deck Calculator

  • Boards run parallel to the house; rows = deck depth ÷ (board width + gap). Nominal 5/4×6 and 2×6 boards are 5.5 in wide.
  • Default joist spacing is 16 in on center, the common maximum for 5/4 wood decking laid perpendicular to joists; composite boards follow the maker's evaluation report.
  • Default waste is 10%; boards and screws are rounded up. The tool does not size joists, beams or footings.

Sources:

  1. International Code Council, 2021 International Residential Code, Chapter 5 (Section R507, Exterior Decks). Deck joist spacing for decking (Table R507.7) and prescriptive deck framing rules.
  2. American Wood Council, DCA 6, Prescriptive Residential Wood Deck Construction Guide. Free guide to code-based deck framing, ledgers and footings.

Flooring Calculator

  • Floor area is length × width per room; stairs are added tread by tread.
  • Default waste is 10%. Makers commonly suggest about 5% for straight lay in simple rooms and 10–15% for diagonal layouts or many cuts.
  • Boxes are rounded up to whole cartons, using the carton coverage you enter.

Sources:

  1. Mullican Flooring (via Lowe's product documents), How to Calculate the Correct Footage When Purchasing Hardwood Flooring. Add about 5% for culling and cuts; 10–15% for diagonal installs.

Tile Calculator

  • Tile count = area ÷ tile face area, plus a pattern allowance: 10% straight, 12% offset, 15% diagonal, 20% herringbone.
  • Thin-set bags use the low end of the maker's coverage range for each trowel notch, so the count errs on the side of enough mortar.
  • Grout is estimated from joint volume (about 0.065 lb per cubic inch, back-calculated from the maker's coverage chart). Everything is rounded up.

Sources:

  1. Custom Building Products, VersaBond Professional Thin-Set Mortar (coverage chart). Square-foot coverage per 50 lb bag by trowel notch.
  2. Custom Building Products, Polyblend Plus Sanded Grout (coverage chart). Coverage per 25 lb bag by tile size and joint width.

Mulch Calculator

  • Volume = bed area × depth; 27 cu ft = 1 cubic yard. Bags are 1.5, 2 or 3 cu ft and are rounded up.
  • The default depth is 3 in. Extension guidance is that fine wood and bark mulches should be no more than 2–3 in deep and kept away from stems and trunks.

Sources:

  1. Clemson Cooperative Extension, Home & Garden Information Center, Mulch (HGIC 1604). Recommended mulch depths and keeping mulch away from stems.

Drywall Calculator

  • Board area = wall and ceiling area minus doors (21 sq ft each) and windows (15 sq ft each); sheets are 4×8, 4×10 or 4×12 ft.
  • Finishing materials per 1,000 sq ft of board, from USG's estimating tables: about 370 ft of paper tape and about 10 gal (138 lb) of ready-mixed all-purpose compound; screws at about 1 per sq ft on 16 in framing. Check the pail label for your compound.
  • Default waste is 10%. Sheets, pails, rolls and screw counts are rounded up.

Sources:

  1. USG, Sheetrock Brand Paper Joint Tape submittal sheet (J1736). Coverage: approx. 370 ft of tape per 1,000 sq ft of gypsum panels; 250 ft rolls.
  2. USG, Sheetrock Brand Installation and Finishing Guide (J371). Measuring and estimating: deduct large openings, convert square footage to panels, and the fastener, joint compound and tape quantity table.
  3. USG, Gypsum Construction Handbook. Reference handbook for gypsum board installation and finishing.

Roofing Calculator

  • Sloped roof area = plan area × slope factor, where slope factor = √(1 + (rise ÷ 12)²).
  • One square = 100 sq ft. Most 3-tab and architectural shingles come 3 bundles per square; heavier lines can be 4 or 5, so check the wrapper and pick 3, 4 or 5 in the tool.
  • Ridge cap defaults to 25 linear ft per bundle (GAF Seal-A-Ridge: 4 bundles cover 100 linear ft); other brands differ, so you can change it.
  • Default waste is 10% (use more for hips and valleys). Squares and bundles are rounded up.

Sources:

  1. GAF, How Many Bundles of Shingles Are in a Square?. A square is 100 sq ft; most asphalt shingles are 3 bundles per square; add 10–15% for waste.
  2. IKO, Cambridge Cool Colors Plus contractor brochure. Example spec: 100 sq ft per 3 bundles (33⅓ sq ft per bundle).
  3. GAF, Seal-A-Ridge Ridge Cap Shingles sell sheet. 4 bundles cover 100 linear feet of hip and ridge.
  4. International Code Council, 2021 International Residential Code, Chapter 9 (Section R905.2, Asphalt Shingles). Code requirements for asphalt shingle roofs (slope, underlayment, fastening).

Fence Calculator

  • Sections = each straight run ÷ post spacing, rounded up. Posts = sections + 1 to end the run + 1 per gate; runs that meet at a corner share the corner post, and a fence that closes on itself needs no end post.
  • Rails: 2 per section for a fence up to 4 ft tall and 3 per section above that. Split rail defaults to 3-rail sections (our default; change it in the tool).
  • Pickets = fence length in inches ÷ (actual board width + gap). The default 1/8 in privacy gap is the space ASTM F537 allows, as stated on the Home Depot cedar fence sheet. Board-on-board uses two layers, with the back boards spaced 4 in apart for 6 in boards. The 5% extra boards is our allowance for culls and cuts.
  • Post holes default to 3× the nominal post width (12 in for a 4×4) and 1/3 of the above-ground height plus a 6 in gravel base (QUIKRETE's minimum). Concrete stops 3 in below grade, the post's own volume is subtracted, and 10% extra is added. Local frost-depth rules override these defaults.
  • Bag yields match the concrete bag calculator: 0.30, 0.375, 0.45 and 0.60 cu ft for 40, 50, 60 and 80 lb bags. Fast-setting post mix lists the same 0.375 cu ft per 50 lb bag.
  • Split rail: line posts about 10 ft 3 in apart, and if you use concrete, 12 in of compacted soil goes under it so the post bottom can drain (Culpeper). No drainage gravel is counted for split rail.
  • Gate hardware, post caps, fasteners and stain are not counted.

Sources:

  1. Lowe's, Fencing Worksheet (How-To Guide). Posts = 1 per 6 or 8 ft section + 1 to end the run + 1 per gate; 2 backer rails per section for 4 ft fences, 3 for 6 ft; pickets = length in inches ÷ picket width (plus spacing). Worked example: 120 ft → 15 sections, 17 posts, 262 pickets.
  2. The Home Depot, Cedar Fence Installation Suggestions. Three rails; 1/8 in between privacy boards per ASTM F537; board/batten privacy fence with bottom boards 4 in apart and top boards over the gaps.
  3. Culpeper Wood Preservers, Split Rail Installation Instructions. Line posts about 10 ft 3 in apart; holes 24–30 in deep; if using concrete, 12 in of soil first and a concrete collar, never concrete under the post.
  4. QUIKRETE, Setting Posts (project instructions). Hole 3× the post width, depth 1/3 to 1/2 of the above-ground post length plus 6 in, 6 in of gravel in the bottom, concrete to 3–4 in below ground level.
  5. QUIKRETE, Fast-Setting Concrete Mix No. 1004 product data sheet. 50 lb bag ≈ 0.375 cu ft, 60 lb ≈ 0.45 cu ft; two 50 lb bags set a 3 in post in a 9 in hole 30 in deep.
  6. QUIKRETE, Concrete Mix No. 1101 product data sheet. Bag yields: 40 lb ≈ 0.30 cu ft, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60 cu ft.

Topsoil Calculator

  • Volume = area × depth (or length × width × depth for each raised bed); 27 cu ft = 1 cubic yard. Bags are 0.75, 1, 1.5 or 2 cu ft and are rounded up.
  • Weight uses 2,050 lb per cubic yard for loose topsoil (about 1.03 short tons). Wet or packed soil is heavier (2,565–3,375 lb in the same chart), so ask your supplier how they weigh it.
  • The settling allowance defaults to 0%. Penn State's 4–6 in lawn figure is a firmed or settled depth, so add some if you are filling to a settled depth.
  • The raised-bed mix of 40% topsoil, 40% compost and 20% soilless mix is one example from University of Illinois Extension, not the only good recipe.

Sources:

  1. Penn State Extension, Lawn Establishment. Typically a minimum of 4 to 6 in (firmed or settled depth) of good-quality topsoil is needed to establish turf.
  2. University of Illinois Extension, Raised Bed Checklist. Beds at least 6–12 in deep, no more than 4 ft wide if reachable from both sides; example mix 40% topsoil, 40% compost, 20% soilless mix.
  3. University of Missouri Extension, Raised-Bed Gardening (G6985). Most plants need at least a 6–12 in rooting zone; beds higher than 18–24 in need retaining walls.
  4. Two Rivers-Ottauquechee Regional Commission (Vermont), Material Weight: Pounds per Cubic Yard. Topsoil 2,050 lb/yd³ loose, 2,565 packed, 3,375 wet.

Paver Calculator

  • Pavers = area × pavers per sq ft, plus the extra for cuts (5% default, our allowance). Pavers per sq ft = 144 ÷ [(length + joint) × (width + joint)]. Joint width defaults to 0 because most pavers have spacer bars; if your paver's maker lists pavers per sq ft, use that.
  • Base depth is a compacted depth: at least 4 in for patios and walks and 6 in for residential driveways on well-drained soil, 2–4 in more in colder climates or on wet or weak soils (ICPI). Bedding sand is 1 in of concrete sand.
  • Base weight uses 3,700 lb per compacted cubic yard (1.85 tons). The loose amount to order uses 2,950 lb per truck-measure yard (about 1.48 tons), both for crushed surfacing base course. Your quarry's figures are better.
  • Bedding sand weight uses 2,750 lb per cubic yard of dry sand. Bags are 0.5 cu ft.
  • Polymeric sand uses the low end of one manufacturer's coverage per 50 lb bag for 2-3/8 in pavers: 65 sq ft for narrow joints and 22 sq ft for wide joints. Other brands and thicker pavers differ, so check the bag.
  • The base area is the paved area. Edge restraints are not counted.

Sources:

  1. Interlocking Concrete Pavement Institute (copy hosted by ORCO Block & Hardscape), ICPI Tech Spec 2: Construction of Interlocking Concrete Pavements. Min. 4 in compacted base for patios and walks, 6 in for residential driveways, 2–4 in thicker for cold, wet or weak soils; 1 in of concrete sand (ASTM C33) bedding; joints 1/16–3/16 in; base compacted in lifts.
  2. Washington State Department of Transportation, Design Manual M 22-01, Chapter 620, Exhibit 620-1 (Unit Dry Weight – Gravel Base and Surfacing). Crushed surfacing base course: 2,950 lb/cy (1.48 T/cy) truck measure, 3,700 lb/cy (1.85 T/cy) compacted.
  3. Alliance Designer Products, Gator Maxx Bond G2 technical data sheet. Coverage per 50 lb bag: 65–85 sq ft for narrow joints, 22–42 sq ft for wide joints (some colors cover less).
  4. Two Rivers-Ottauquechee Regional Commission (Vermont), Material Weight: Pounds per Cubic Yard. Dry sand 2,750 lb/yd³.

Asphalt Calculator

  • Tons = area × compacted thickness × density ÷ 2,000, with a default of 145 lb/ft³ of compacted mix (108.75 lb/sy/in). Use your plant's figure if you have it.
  • The default 5% extra is a CalcTheJob allowance, not an industry standard. Base stone uses 1.85 tons per compacted and 1.48 per loose cubic yard.
  • The cost line is your price × tons of mix only. This is a quantity estimate, not a pavement design.

Sources:

  1. Pennsylvania Asphalt Pavement Association / Penn State Superpave Center, Constructing Quality Asphalt Pavements checklist booklet (2025). Compacted mix typically 108–120 lb/sy/in (144–160 lb/cf); 150 × 300 ft lot at 3 in = 825 tons at 110 lb/sy/in; in-place density about 94% of maximum.
  2. Michigan Department of Transportation, 501 – Plant Produced Hot Mix Asphalt (Construction Manual). Yield check rule: 110 pounds per square yard = 1 inch of thickness; application-rate table by thickness.
  3. Colorado Asphalt Pavement Association, Asphalt Driveways technical brief (2020). Minimum residential designs: 4.5–5.5 in full-depth, or 3 in of asphalt over 4–6 in of aggregate base, by subgrade; surface slope at least ¼ in per foot; overlays typically 1.5–2 in.
  4. Asphalt Institute (Colorado APA brief), “Best Practices” for the Use of Asphalt Driveways. 6–8 in of crushed aggregate base is usually adequate, with a 2 in bottom course and a 1.5 in surface course.
  5. Illinois Asphalt Pavement Association, Driveways. 4 in of full-depth asphalt may be adequate, 5–6 in is stronger; placing in lifts; overlays of 1.5–2 in.
  6. Washington State Department of Transportation, Design Manual M 22-01, Chapter 620, Exhibit 620-1 (Unit Dry Weight – Gravel Base and Surfacing). Crushed surfacing base course: 2,950 lb/cy (1.48 T/cy) truck measure, 3,700 lb/cy (1.85 T/cy) compacted.

Roof Pitch Calculator

  • Pitch = 12 × rise ÷ run; angle = arctan(rise ÷ run); percent slope = 100 × rise ÷ run. These are exact geometric conversions.
  • Pitch multiplier = √(1 + (rise ÷ run)²); hip/valley factor = √(2 + (rise ÷ run)²) for a regular hip roof with equal pitches (45° in plan).
  • Rafter length is the line length from the outside of the wall to the ridge centerline for a symmetrical gable (run = half the span). It does not deduct half the ridge board or add plumb and bird's-mouth cuts.
  • The shingle and safety notes summarize the code and OSHA thresholds below; local codes and the shingle maker's instructions govern.

Sources:

  1. City of Seattle, Department of Construction and Inspections, 2018 Seattle Residential Code, Chapter 9 Roof Assemblies (adopts IRC Section R905.2.2). R905.2.2: asphalt shingles only on slopes of 2:12 or greater; double underlayment required from 2:12 up to 4:12.
  2. U.S. Occupational Safety and Health Administration, 29 CFR 1926.500, Fall Protection: Scope, application, and definitions. Low-slope roof: slope less than or equal to 4 in 12; steep roof: slope greater than 4 in 12.

Paint Calculator

  • Wall area = room perimeter × wall height, minus 21 sq ft per door and 15 sq ft per window (the same allowances as our drywall calculator). Measure large openings separately.
  • The default coverage is 350 sq ft per gallon per coat, the low end of the 350–400 sq ft/gal printed on several Sherwin-Williams interior latex data sheets at 4 mils wet. Textured or porous surfaces cover less; your can's label wins.
  • Gallons = area × coats ÷ coverage. Cans are rounded up to whole quarts; three or more quarts are rounded up to another gallon.
  • Primer is one coat at 400 sq ft per gallon (Sherwin-Williams Premium Wall & Wood Primer data sheet). Trim, doors and cabinets are not included.

Sources:

  1. Sherwin-Williams, Duration Home Interior Latex Flat (A95 Series) product data sheet. Coverage 350–400 sq ft per gallon at 4 mils wet, 1.6 mils dry; drywall: self-prime with 2 coats, or 1 coat of primer plus 2 coats.
  2. Sherwin-Williams, Premium Wall & Wood Interior Latex Primer (B28W08111) product data sheet. Coverage 400 sq ft per gallon at 4 mils wet, 1.5 mils dry.
  3. Benjamin Moore, Regal Select Interior technical data sheet. Spread rate 400–450 sq ft per gallon.
  4. Benjamin Moore, How to Choose the Best Paint Primer. A previously painted surface in good condition most likely does not need primer; prime bare substrates, stains and rust, dramatic color changes and hard-to-coat surfaces.

Sand Calculator

  • Volume = area × depth; 27 cu ft = 1 cubic yard. Circles use π × radius².
  • Loose weights: dry sand 2,750 lb per cubic yard (1.375 tons), wet sand 3,300 lb (1.65 tons). Your supplier's figure is better.
  • Compacted fill: compacted sand is taken as about 3,400 lb per cubic yard, so the loose volume to order is the compacted volume × 3,400 ÷ 2,750 ≈ 1.24.
  • Bags hold about 0.5 cu ft (50 lb). Bag counts are rounded up. The default 5% extra is a CalcTheJob allowance for spillage and uneven ground.
  • Playground depths are quoted from the CPSC handbook for non-impact-tested sand; this calculator does not certify a safety surface.

Sources:

  1. Two Rivers-Ottauquechee Regional Commission (Vermont), Material Weight: Pounds per Cubic Yard. Dry sand 2,750 lb/yd³; wet sand 3,300 lb/yd³.
  2. Washington State Department of Transportation, Design Manual M 22-01, Chapter 620, Exhibit 620-1 (Unit Dry Weight – Gravel Base and Surfacing). Gravel base compacted weight 3,400–3,800 lb/cy; the factor approaches 3,400 lb/cy (1.70 T/cy) for material that is essentially all sand.
  3. QUIKRETE, Play Sand (No. 1113) tear pad with play-box calculator. 50 lb bag contains approx. ½ cu ft; for play boxes and under swing sets; bags needed by box size and depth (e.g. 6 × 6 ft at 6 in = 36 bags).
  4. QUIKRETE, Sand & Gravel Products data sheet. All-Purpose Sand meets ASTM C33 and is sold for concrete, underlayment for brick pavers and traction; Premium Play Sand is washed and screened for sandboxes.
  5. U.S. Consumer Product Safety Commission, Public Playground Safety Handbook (2025). Table 2: sand 12 in installed / 9 in compressed protects to a 4 ft critical height; loose fill compresses at least 25%; never maintain less than 9 in.

Review and corrections

Sources were last checked on October 25, 2026. When a manufacturer changes a product or a link moves, we update the calculator and its dates. Spotted an error? Email contact@calcthejob.com.