Tile Calculator

How to use this calculator

1. Choose how many rectangles make up the area (up to three) and enter each one’s length and width in feet. Use decimals for inches: 10 ft 6 in is 10.5.
2. Pick the tile size, or choose Custom size and enter it in inches.
3. Pick the grout joint width and the layout. Each layout sets a waste allowance; choose Custom waste % to set your own.
4. Enter the coverage per box, printed on the carton in square feet.
5. Under Grout and prices, adjust the tile thickness (it sets the joint depth for grout) and the example prices.

The result gives the number of tiles including waste, the boxes to buy and an estimated cost, with the grout in pounds and the tiles per box below. The table compares the three layouts for your room.

The formulas

Each tile covers its own area plus its share of the grout joint. Divide the floor area by that and add the waste allowance:

Here L and W are the tile’s length and width and j is the joint, all in inches; the area is in square feet. Boxes are the tiles divided by the tiles per box, rounded up.

Grout uses the formula found on manufacturers’ coverage charts. The joint volume per square foot is 144 × joint width × joint depth × (L + W) ÷ (L × W) cubic inches, with the depth taken as the tile thickness. The calculator converts that to pounds of grout powder at 0.058 lb per cubic inch, which reproduces MAPEI’s published coverage for its Keracolor S sanded grout: a 25 lb bag covers 383 square feet of 12 × 12 × 3/8 inch tile with 1/8 inch joints. Then it adds 10% for waste, spillage and clean-up, as LATICRETE recommends.

Worked example

The default is a 12 × 10 foot floor (120 sq ft) of 12 × 24 inch porcelain with 1/8 inch joints, laid straight:

1. Each tile covers (24.125 × 12.125) ÷ 144 = 2.0314 sq ft with its joint.
2. Tiles: 120 ÷ 2.0314 = 59.07, plus 10% = 64.98, so 65 tiles.
3. Boxes: at 16 sq ft per box, 8 tiles per box, so 65 ÷ 8 rounds up to 9 boxes (144 sq ft).
4. Grout: 144 × 0.125 × 0.375 × 36 ÷ 288 = 0.844 cu in per sq ft, × 120 = 101.25 cu in, × 0.058 lb = 5.87 lb, plus 10% = 6.46 lb.
5. Cost at the example prices of $3.50 per sq ft and $25 a bag of grout: 144 × $3.50 + $25 = $529.

The same floor laid in herringbone needs 71 tiles, still 9 boxes. Add an 8 × 5 foot hallway as a second area and the total grows to 160 sq ft, 87 tiles and 11 boxes; diagonal or herringbone would take 12 boxes.

Tiles and grout per 100 square feet

For 100 sq ft with 10% waste, 1/16 inch joints for tiles under 12 inches and 1/8 inch for larger ones (grout at 5/16 inch thickness for small tile and 3/8 inch for 12 inch and up, with 10% extra):

Small tiles need far more grout per square foot because there are more joints. A wider joint raises grout in proportion: 3/16 inch takes half again as much as 1/8 inch.

Waste allowance by layout

These follow the guidance of Italian porcelain manufacturer Keope, which also suggests about 5% more for large-format tile, where each broken or miscut piece is a bigger loss. Retailers’ recommendations vary, and some suggest more for complex patterns, so if your room has many corners, a niche or a floor drain, lean higher.

Tips for buying tile

• Buy everything at once, from the same lot. Tile color and size can vary slightly between production lots. Check that the lot numbers on the cartons match.
• Keep a spare box. A cracked tile five years from now is easy to replace if you have the same lot in the garage, and the product may be discontinued by then.
• Measure the real tile. Rectified porcelain is often slightly smaller than its nominal size; the box coverage reflects the real size, which is why it may say 15.5 rather than 16 sq ft.
• Don’t forget the rest. Thinset mortar, backer board, membrane, trim and spacers are separate. For the room’s total floor area, the square footage calculator handles odd shapes, and if you’re tiling stair treads, the stair calculator gives the tread count and depth.

Assumptions and limitations

• Areas are rectangles; split L-shaped rooms into pieces. The tile count includes the grout joint around each tile.
• Waste percentages are planning allowances, not guarantees. Patterned and natural-stone tile, and rooms with many obstacles, can need more.
• Grout uses the joint width and tile thickness you enter and a powder yield calibrated to one manufacturer’s sanded grout. Real use varies with joint consistency and tile texture, so check the coverage chart on the bag you buy. Epoxy and urethane grouts have different yields.
• Prices are editable examples as of November 2026, not quotes.

Sources

• Keope: Tile calculation, a practical guide for floors and walls (waste by layout)
• MAPEI: Keracolor S sanded grout installation instructions and coverage chart (PDF)
• LATICRETE: Project estimator and grout coverage guidelines
• Custom Building Products: Technical Bulletin 89, Grout coverage rates (PDF)

Updated November 2026. Results are estimates for educational purposes and depend on the inputs you provide.