How do I calculate how much grout I need?

Enter tile width, tile length, grout joint width, tile thickness, and total area. The calculator uses the grout volume formula to determine bag count based on standard bag sizes and shows estimated material cost.

What is the formula for grout coverage?

Grout volume equals tile width plus tile length, times joint width, times tile thickness, times 1.2 for waste, all divided by tile width times tile length, then multiplied by total area. The calculator handles this math and outputs bag counts directly.

How many square feet does a bag of grout cover?

Coverage varies by tile size and joint width. Larger tiles with narrow joints use less grout; small tiles with wide joints use more. Enter your tile and joint specs into the calculator to see the exact bag count and cost for your project.

Flooring

Grout Coverage Calculator

Estimate grout bag counts and cost based on tile size, grout joint width, tile thickness, and total area.

Use this free grout calculator to estimate how much grout your tile project needs before you open a bag. Enter tile size, joint width, tile thickness, project area, bag size, and waste allowance, then get a practical material estimate for floors, walls, backsplashes, showers, and other tiled surfaces.

How it works

The calculator estimates grout by treating each tile joint as a small volume that needs to be filled. The core formula is: grout lbs per sq ft = ((tile L + tile W) / (tile L × tile W)) × joint width × tile thickness × 144 × density factor. Tile length, tile width, joint width, and tile thickness are entered in inches. The 144 converts the result to a square foot basis, and the density factor converts grout volume into pounds. After that, the calculator multiplies by the total project area, adds your waste allowance, then divides by the bag size so you know how many bags to buy.

Worked examples

12 in x 12 in tiles, 3/16 in joints, 0.3 in thick across 100 sq ft, using a 0.065 density factor, 10% waste, and 25 lb bags: ((12 + 12) / (12 × 12)) × 0.1875 × 0.3 × 144 × 0.065 = about 0.088 lb per sq ft. 0.088 × 100 = 8.8 lb, plus 10% waste = 9.7 lb, so buy 1 bag.
3 in x 6 in subway tiles, 1/8 in joints, 0.25 in thick across 80 sq ft, using a 0.065 density factor, 10% waste, and 25 lb bags: ((3 + 6) / (3 × 6)) × 0.125 × 0.25 × 144 × 0.065 = about 0.146 lb per sq ft. 0.146 × 80 = 11.7 lb, plus 10% waste = 12.9 lb, so buy 1 bag.
2 in x 2 in mosaic tiles, 1/8 in joints, 0.25 in thick across 120 sq ft, using a 0.065 density factor, 10% waste, and 25 lb bags: ((2 + 2) / (2 × 2)) × 0.125 × 0.25 × 144 × 0.065 = about 0.293 lb per sq ft. 0.293 × 120 = 35.1 lb, plus 10% waste = 38.6 lb, so buy 2 bags.

FAQ

Why do smaller tiles usually need more grout?

Smaller tiles create more grout joints across the same area. More joint length means more space to fill, so mosaics and subway tile patterns often need more grout than large-format tile.

Should I include a waste allowance?

Yes. A waste allowance helps cover cleanup loss, uneven joints, surface texture, and small measuring errors. It's especially useful for rough tile, complex layouts, and first-time installations.

Does joint width change the grout estimate a lot?

Yes. Wider joints increase the volume of grout between tiles. Even a small change in joint width can noticeably change the final amount, especially across a full floor or shower wall.

How do I know what bag size to enter?

Use the weight printed on the grout package. If your grout is sold in different bag sizes, run the calculator with the size you plan to buy so the bag count matches the product on the shelf.