Grout Calculator
Calculate how much tile grout you need. Enter your area, tile size, thickness and joint width to get grout weight, volume and the number of 25 lb bags.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the Grout Calculator Works
Grout fills the joints between your tiles, and the amount you need depends on far more than just the floor area. This calculator uses the standard tile-grout estimating formula, taking your tiled area, tile length and width, tile thickness and joint width to return grout volume, total weight, and the number of 25 lb bags to buy.
The Formula
Grout fills the perimeter joints around every tile. The volume of grout per square foot of tile is:
Grout volume per sq ft (in³) = ((tile L + tile W) ÷ (tile L × tile W)) × joint width × tile thickness × 144
All tile measurements are in inches. Multiply by your area in square feet, then convert volume to weight using dry grout density of about 0.0581 lb per in³ (roughly 100 lb per cubic foot), and finally add a waste allowance.
Worked Example
A bathroom floor of 100 sq ft uses 12 × 12 in tiles that are 3/8 in (0.375) thick, set with 1/8 in (0.125) joints, with 10% waste:
- Volume per sq ft = ((12 + 12) ÷ (12 × 12)) × 0.125 × 0.375 × 144 = 1.125 in³/sq ft
- Total volume = 1.125 × 100 = 112.5 in³ = ≈ 0.065 ft³
- Weight = 112.5 × 0.0581 × 1.10 = ≈ 7.2 lb
- Bags = 7.2 ÷ 25, rounded up = 1 bag
Grout Usage by Tile Size
Smaller tiles dramatically increase grout usage at the same joint width and area:
| Tile size | Joint width | Approx. grout per 100 sq ft |
|---|---|---|
| 24 × 24 in | 1/8 in | ≈ 3.3 lb |
| 12 × 12 in | 1/8 in | ≈ 6.5 lb |
| 6 × 6 in | 1/8 in | ≈ 13 lb |
| 2 × 2 in (mosaic) | 1/8 in | ≈ 39 lb |
Tips for Buying Grout
- Match sanded vs. unsanded grout to your joint — use sanded for joints 1/8 in and wider, unsanded for narrower joints.
- Buy from one lot to avoid color variation between batches.
- Keep a small reserve for future repairs in the same color.
Frequently asked questions
How do I calculate how much grout I need?+
Find the grout volume per square foot using ((tile length + tile width) ÷ (tile length × tile width)) × joint width × tile thickness × 144, with all tile measurements in inches. Multiply by your total tiled area, convert to weight using grout density of about 0.0581 lb per cubic inch, then add 10% for waste.
How much area does a 25 lb bag of grout cover?+
It depends on tile size, joint width and tile thickness. As a guide, a 25 lb bag of dry grout covers roughly 200 square feet of 12 by 12 inch tile with 1/8 inch joints, but only about 40 to 60 square feet of small mosaic tile with the same joints, because smaller tiles have far more joint length per square foot.
Why do smaller tiles need more grout?+
Grout fills the joints between tiles, and smaller tiles pack more joint length into each square foot. The formula captures this through the (tile length + tile width) ÷ (tile length × tile width) term, which grows as tiles get smaller, so mosaics and subway tiles consume much more grout than large-format tiles.
Does joint width change how much grout I need?+
Yes, directly. Grout usage scales linearly with joint width, so a 3/16 inch joint uses 50% more grout than a 1/8 inch joint over the same tile and area. The joint depth, which equals the tile thickness, also matters: thicker tiles create deeper joints that hold more grout.
Should I buy extra grout?+
Yes. Add about 10% to your calculated amount to cover mixing waste, uneven substrates, joints that are slightly wider than planned, and the grout left clinging to your float and bucket. Buying one extra bag from the same lot also protects you against slight color differences between manufacturing batches.