Tile Grout Calculator - How Much Grout Do I Need?

How the grout estimate works

Grout quantity depends on the empty space between tiles, not just the square footage. The joint width, grout joint depth, tile length, and tile width determine how much void space must be filled. Small subway tile and mosaic sheets have many more joint lines per square foot than large-format porcelain tile, so they usually need much more grout for the same floor, wall, shower, or backsplash area.

This calculator first estimates grout volume from tile geometry, then converts that volume into dry mix weight using the selected grout density. It adds the waste allowance, rounds up to whole bags or containers, and shows the leftover margin. If your product label gives a specific coverage rate per bag, enter it as a yield override; the tool will use that as an additional bag-count check.

Grout depth often matches tile thickness, but it is not always the same. Shallow joints, backer rod, mosaics, thick tile, and some edge profiles can change the actual filled depth. Use the editable grout joint depth field for the depth you expect to fill rather than assuming the full tile thickness.

Manufacturer yield varies by product chemistry, tile edge profile, surface texture, installation method, and cleanup loss. Use this as a practical purchase estimator, then compare the result with the chosen product's coverage chart before buying.

Formula

1. Convert all tile dimensions to the same length unit. In imperial mode, area is converted from square feet to square inches.
2. Name the variables: A = area, L = tile length, W = tile width, J = joint width, and D = grout joint depth.
3. Estimate grout volume: V = A x J x D x (1 / L + 1 / W).
4. Convert volume: gallons = cubic inches / 231, or liters = gallons x 3.78541.
5. Estimate dry mix: dry weight = volume x grout density.
6. Add waste: required dry mix = dry weight x (1 + waste % / 100).
7. Convert to bags: bags = ceiling(required dry mix / bag size). If a product yield per bag is entered, the calculator also checks ceiling(area with waste / product yield) and uses the higher bag count.

Worked example

With the default inputs, a 100 sq ft floor uses 12x12 in tile, 1/8 in joints, 0.35 in grout depth, sanded grout at 12 lb/gal, 10% waste, and a 10 lb bag. The estimated grout volume is about 0.45 gal. Dry mix before waste is about 5.45 lb, and the 10% waste allowance raises the required dry mix to about 6.0 lb. Since bags are rounded up, the recommendation is to buy 1 x 10 lb bag, leaving roughly 4.0 lb of margin.

Common tile examples

Approximate dry mix for 100 sq ft with 10% waste and 12 lb/gal density. Bag counts assume 10 lb bags.

FAQs

How much grout do I need for 100 sq ft?

For 100 sq ft of 12x12 in tile with 1/8 in joints and 0.35 in grout depth, the default estimate is about 5.5 lb before waste or 6.0 lb with 10% waste. Smaller tile and wider joints increase the amount.

How much waste should I add?

Use 10% for a normal layout. Increase to 15% or more for mosaics, textured tile, irregular joints, difficult cleanup, or when you want more margin for color consistency.

Should I use sanded or unsanded grout?

Unsanded grout is commonly used for narrow joints such as 1/8 in or less. Sanded grout is commonly used for wider joints. Always follow the manufacturer's joint-width limits.

What is grout depth versus tile thickness?

Tile thickness is the physical tile thickness. Grout depth is the depth of the open joint that will actually be filled. Use grout depth when joints are shallow, backed, or different from full tile thickness.

Can I use this for mosaic tile?

Yes. Enter the individual mosaic tile size, not the sheet size. Mosaics have more joint lines per square foot, so their grout use is usually much higher.

How much grout for 12x24 tile?

A 100 sq ft area of 12x24 in tile with 3/16 in joints and 0.35 in grout depth needs about 6.8 lb with 10% waste using the default density.

Does shower grout differ from floor grout?

The quantity formula is the same for showers, walls, floors, and backsplashes. Product choice differs because wet areas need grout and sealant systems rated for that use.

How do I convert the estimate into bags?

Add waste to the dry mix estimate, divide by the bag or container size, and round up. The calculator does this automatically and shows the leftover margin.

Limitations

Real coverage varies by tile edge profile, grout density, product chemistry, surface texture, cleanup loss, installer technique, and manufacturer yield. Use product-specific coverage data when it is available.

Disclaimer

Results are estimates. Verify grout coverage with manufacturer data and add a waste factor for cleanup and mixing loss.