How to use the grout and thinset calculator
- Enter the tiled area in square feet. For walls, multiply width by tiled height. If you have not worked out the tile count yet, start with the tile calculator. It gives quick grout and thinset numbers too, while this page goes into more detail.
- Grout mode: enter the tile length, width and thickness, then the joint width. Grout depth is taken as the full tile thickness.
- Pick a density preset. One matches MAPEI’s Ultracolor Plus FA chart, the other CUSTOM’s Polyblend Plus sanded chart. If your grout is a different brand, pick either one and compare the result with the chart on your bag.
- Thinset mode: pick the product chart and the trowel notch you plan to use. The result is the number of 50 lb bags.
How much grout do I need? The formula
Grout (lb) = area × lb per sq ft × (1 + extra)
Coverage per bag (sq ft) = bag weight ÷ lb per sq ft
L and W are the tile’s length and width in inches, and the joint width and depth are also in inches. The (L + W) ÷ (L × W) part is the length of joint per square inch of tile. That is why small tiles take far more grout: a 1 × 1 in mosaic has 2 inches of joint for every square inch of tile, while a 12 × 12 tile has only 1/6 inch.
We checked the formula against the manufacturers’ charts. A density of 98.5 lb per cubic foot reproduces the MAPEI Ultracolor Plus FA chart to within 2% on every cell we tested. For example, 12 × 12 × ⅜ in tile with ⅛ in joints gives 156 sq ft per 10 lb, the same as the chart. CUSTOM’s sanded Polyblend Plus chart implies a denser mix, about 110 lb per cubic foot, and matches to within about 6%.
Grout coverage chart
Square feet covered by a 10 lb bag of MAPEI Ultracolor Plus FA, from the manufacturer’s data sheet. Multiply by 2.5 for a 25 lb bag.
| Tile (in) | 1/16″ | 1/8″ | 3/16″ | 1/4″ | 3/8″ |
|---|---|---|---|---|---|
| 1 × 1 × ¼ | 39 | 20 | 13 | 10 | 7 |
| 2 × 2 × ¼ | 78 | 39 | 26 | 20 | 13 |
| 6 × 6 × ¼ | 233 | 117 | 78 | 59 | 39 |
| 12 × 12 × ⅜ | 311 | 156 | 104 | 78 | 52 |
| 12 × 24 × ⅜ | 414 | 207 | 138 | 104 | 69 |
| 18 × 18 × ⅜ | 466 | 233 | 156 | 117 | 78 |
| 24 × 24 × ⅜ | 621 | 311 | 207 | 156 | 104 |
Worked examples
A 100 sq ft floor of 12 × 12 × ⅜ in tile with ⅛ in joints. At 0.064 lb per sq ft that is 6.4 lb, or 7.1 lb with 10% extra. One 10 lb bag covers it.
A 30 sq ft backsplash of 2 × 2 in mosaic, ¼ in thick, with ⅛ in joints. Mosaics are grout-hungry: 0.26 lb per sq ft, or 7.7 lb, which rises to 8.5 lb with extra. That is more grout than the whole 100 sq ft floor above.
200 sq ft of 24 × 24 × ⅜ in porcelain with ⅛ in joints. Only 0.032 lb per sq ft, so 7.1 lb with extra. Large tiles save grout but need more thinset (see below).
How much thinset do I need?
Thinset coverage depends on the trowel notch, not the tile size. A deeper notch leaves more mortar under each tile. Coverage per 50 lb bag from the two charts we use:
| Trowel notch | CUSTOM VersaBond | MAPEI Ultraflex 2 |
|---|---|---|
| ¼ × ¼ in square | 90–100 sq ft | 75–90 sq ft |
| ¼ × ⅜ in square | 60–67 sq ft | 55–65 sq ft |
| ½ × ½ in square | 42–47 sq ft | — |
| ¾ × 9/16 in U-notch (45°) | 34–38 sq ft | — |
The calculator divides your area by the low end of the range, so you will not run short. The “best case” figure uses the high end. For example, 100 sq ft with a ¼ × ⅜ in notch is 100 ÷ 60 = 1.7, so 2 bags of VersaBond. 200 sq ft of large-format tile with a ½ × ½ in notch is 200 ÷ 42 = 4.8, so 5 bags.
Choose the notch that gives full contact, not the one that stretches the bag. MAPEI’s data sheet calls for more than 80% mortar contact indoors and more than 95% outdoors and in wet areas. It adds that back-buttering the tile may be needed to get there. CUSTOM notes that large tiles, tiles with deep patterns on the back, and natural stone may need a bigger notch plus back-troweling, and that the extra mortar should be added to your estimate. Lift a tile now and then to check contact.
Grouting tips that affect quantity
- Clean the joints. MAPEI says to remove thinset so that at least ⅔ of the tile depth is open for grout.
- Check the joint range. Every grout is made for a range of joint widths. Ultracolor Plus FA, for example, is listed for 1/16 to 3/4 in joints.
- Buy the same color lot. If the job needs several bags, buy them together.
- Plan the rest of the room. If you are redoing a bathroom, the drywall calculator and flooring calculator cover the rest of the room.
Sources & assumptions
How this calculator gets its numbers. Full method: our methodology.
- Grout (lb per sq ft) = (L + W) ÷ (L × W) × joint width × joint depth × 144 × density ÷ 1,728, with tile sizes in inches and depth equal to tile thickness.
- Density presets are back-calculated from coverage charts: about 98.5 lb/ft³ reproduces the MAPEI Ultracolor Plus FA chart to within 2% on the cells we tested; about 110 lb/ft³ matches the CUSTOM Polyblend Plus sanded chart to within 6%.
- A default 10% extra is added to grout (our allowance), and bags are rounded up.
- Thinset bags = area ÷ the LOW end of the maker’s coverage range for the trowel notch, so the count errs on the side of enough mortar. The best case uses the high end. Back-troweling is not included.
Sources
- MAPEI, Ultracolor Plus FA technical data sheet. Coverage per 10 lb by tile size and joint width (1/16 to 3/4 in); 10 and 25 lb packages.
- Custom Building Products, Polyblend Plus Sanded Grout (coverage chart). Coverage per 25 lb and 7 lb bag by tile size and joint width.
- Custom Building Products, VersaBond Professional Thin-Set Mortar (coverage chart). Sq ft per 50 lb bag: ¼ × ¼ in 90–100, ¼ × ⅜ in 60–67, ½ × ½ in 42–47, ¾ in U-notch at 45° 34–38.
- MAPEI, Ultraflex 2 technical data sheet. Sq ft per 50 lb: ¼ × ¼ in 75–90, ¼ × ⅜ in 55–65; leave ⅔ of the tile depth open for grout; 80% / 95% contact.
Last reviewed . Product figures vary by brand; the label on what you buy wins.
Frequently asked questions
How much grout do I need for 100 square feet?
For 12 by 12 inch tile 3/8 inch thick with 1/8 inch joints, about 6.4 lb, or 7 lb with 10% extra, so one 10 lb bag. Smaller tile or wider joints need much more.
How many square feet does a 25 lb bag of grout cover?
It depends on tile size and joint width. With 12 by 12 inch tile and 1/8 inch joints, about 390 sq ft by the MAPEI chart and 348 sq ft by the CUSTOM sanded chart. With 2 by 2 inch mosaic it can be under 100 sq ft.
How do you calculate grout?
Multiply (tile length + tile width) ÷ (length × width) by the joint width and depth, all in inches, then by 144 to get cubic inches of grout per square foot. Multiply by the grout density and the area.
How much thinset do I need for 100 square feet?
With a 1/4 by 3/8 inch square-notch trowel, plan on 2 bags of 50 lb thinset (about 60 to 67 sq ft per bag). With a 1/4 by 1/4 inch notch, one to two bags.
Do large tiles need more thinset?
Yes. They need a deeper notch, such as 1/2 by 1/2 inch at about 42 to 47 sq ft per bag, and often back-troweling, which adds more.