Grout Calculator

How to use the Grout Calculator

1. Choose Inches & sq ft or Metric (mm, m²).
2. Enter the Tile length, Tile width and Tile thickness. Measure an actual tile, since the size on the box can be rounded. Fractions such as 3/8 or 4 1/4 work.
3. Pick the Grout joint width, from 1/16 in to 1/2 in, or choose Custom.
4. Enter the Area to grout, the floor or wall area you are tiling.
5. Set a Waste allowance. The default is 10%; MAPEI's online grout calculator suggests adding 5% to 10% extra.
6. Enter your Bag size and, if you know it, a Grout density that matches your product (see below). Add a Price per bag for a cost estimate, then press Calculate.

Grout calculator formula

Every tile adds half its perimeter, L + W, of joint to the floor. Divide by the tile's area and you get joint length per unit of floor. Multiply by the joint width and depth to get joint volume, then by density to get weight.

About density. D is the weight of grout powder needed to fill a given volume of joint. MAPEI's data sheet for Keracolor GG grout gives the consumption formula kg/m² = (A + B) ÷ (A × B) × C × D × 1.6, with all sizes in mm. That 1.6 factor equals 1,600 kg/m³, or about 100 lb/ft³, which is the calculator's default. It is not the same as the density of the mixed grout, which the same data sheet lists separately as 2,000 kg/m³, so use the coverage-based value.

Example: 300 sq ft of 12 × 12 tile with 3/16 in joints

A kitchen and family-room floor has 300 sq ft of 12 × 12 × 3/8 in porcelain tile with 3/16 in joints. The grout comes in 25 lb bags, and the plan adds 10% for waste.

1. Joint factor: (12 + 12) ÷ (12 × 12) = 0.1667 per in.
2. Joint depth per area: 0.1667 × 3/16 × 3/8 = 0.01172 in, or 1.6875 cu in of joint per sq ft.
3. Weight per sq ft: 1.6875 × 100 ÷ 1,728 = 0.0977 lb.
4. Before waste: 0.0977 × 300 = 29.30 lb.
5. With 10% waste: 29.30 × 1.10 = 32.23 lb (14.62 kg).
6. Bags: 32.23 ÷ 25 = 1.29, rounded up to 2 bags.

One 25 lb bag covers 25 ÷ 0.0977 = 256 sq ft before waste. MAPEI's Keracolor S chart lists 253 sq ft for the same tile and joint, about 1% less.

Using a manufacturer's coverage chart

Grout makers publish coverage charts on their technical data sheets, and MAPEI also offers its own Tile Grouts Calculator. CalcEagle is independent and not affiliated with MAPEI or any other grout maker. To read a chart:

1. Find the row for your tile size and thickness.
2. Find the column for your joint width. The cell is the area one bag covers.
3. Divide your area by that coverage, add waste, and round up to whole bags.

Here is how this calculator, at its default 100 lb/ft³, compares with MAPEI's Keracolor S chart (sq ft per 25 lb bag):

Charts from other brands can differ. Custom Building Products' Polyblend Plus chart lists 348 sq ft per 25 lb bag for 12 × 12 × 3/8 in tile with 1/8 in joints, about 9% less than MAPEI's 383. To match a specific chart, scale the density: 100 × (calculator coverage ÷ chart coverage). For that Polyblend Plus cell, 100 × 384 ÷ 348 ≈ 110 lb/ft³.

How to read the result

• Grout to buy is the number of bags, rounded up, including your waste allowance.
• Grout per sq ft and Coverage per bag let you check the answer against your product's chart before you buy.
• Joint width and tile thickness scale the answer directly. Doubling the joint width doubles the grout, and a 1/2 in thick tile needs one-third more grout than a 3/8 in tile of the same size.

Assumptions and limitations

• Joints are filled to the full tile thickness, which is also how the MAPEI chart figures compare. MAPEI's instructions call for clearing about two-thirds of the tile depth for grout, so real use is often a little lower.
• All tiles are the same rectangular size. Layout pattern does not change the result, because each tile contributes the same length of joint. Hexagons, mixed-size patterns and irregular stone are not modeled.
• Small mosaics with wide joints use more grout than the formula predicts in MAPEI's chart (for example, 14 vs. 16 sq ft per bag for 1 × 1 in tile with 3/8 in joints), so add extra waste for mosaics.
• The default density comes from MAPEI's cement grout formula. Other brands' charts imply roughly 5% to 10% more grout for the same joints, and epoxy or other non-cement grouts need their own chart.
• Results are estimates. Confirm with the coverage chart on your grout's data sheet.

Common mistakes

• Using the wrong grout type for the joint. MAPEI says its Keracolor S sanded grout should not be used in joints narrower than 1/8 in, and Custom notes that non-sanded grout may suit joints up to 1/8 in. Custom also recommends testing sanded grout on a small area, because it can scratch some tile.
• Leaving out tile thickness. Thicker tile means deeper joints and more grout.
• Grouting with uneven joints. If spacers drift, measure the actual joint width before you buy.
• Mixing bags separately. If you use more than one bag at a time, MAPEI and Custom both say to dry-blend the powder first so the color stays even.

Planning more of the project? The Brick Calculator counts brick and mortar for a wall, and the Drop Ceiling Calculator estimates a suspended ceiling grid. For a quick markup or tax figure, use the Percentage Calculator.

Formulas and content last reviewed on October 13, 2026. Last updated October 13, 2026. Results are estimates for general information only. Spotted a problem? Tell us and we will check it.