How many 12" tiles in a square foot?

One. A 12-inch tile covers exactly 1 ft². For a 120 ft² floor with 10% waste, plan for 132 tiles.

How much thinset do I need?

Roughly one 50-lb bag per 40–60 ft² with a 1/4-inch square-notch trowel. Large-format tile needs a bigger notch and drops coverage to about 30 ft² per bag, so trowel size matters more than tile size in the calculation.

What size notched trowel should I use?

Match the notch to the tile: 1/4-inch square notch for tile up to 8 inches, 1/4 × 3/8 for 8–16 inches, and 1/2-inch for large-format. The goal is 80% mortar coverage on the tile back for a dry area and 95% in a wet one.

How wide should tile grout lines be?

One-sixteenth to 1/8 inch for rectified tile, 3/16 for standard ceramic, and 1/4 or wider for handmade or slate. Anything under 1/8 inch needs unsanded grout; sanded grout will not compact into a joint that narrow.

How long before I can walk on new tile?

Twenty-four hours before light foot traffic and 48 to 72 hours before grouting, though fast-setting mortars cut that. Walking on tile before the mortar cures breaks the bond, and the tile will sound hollow long after it looks fine.

Do I need backer board under tile?

On a floor, yes, unless the subfloor is concrete — cement board or an uncoupling membrane over plywood. Deflection is what cracks tile and grout, and drywall or bare plywood moves far more than tile can tolerate.

Should I start tiling from the centre or a wall?

Lay out from the centre lines, then adjust so you do not end with a sliver at any visible edge. Snap your lines first and dry-lay a row in both directions — a layout that leaves a half tile at the door is far better than a quarter-inch strip at the tub.

How much tile do I need?

Measure the floor or wall area in square feet and add 10 percent for waste. The waste factor is not padding — it covers the cuts at every edge, the tiles that break during cutting, and the spares you will want years later when one cracks and the run has been discontinued. Push it to 15 percent for a diagonal or herringbone layout, which cuts every perimeter tile and produces offcuts that rarely fit anywhere else. Tile is sold by the box rather than the tile, so divide by the square footage per box and round up. Buy every box from the same production lot: shade varies noticeably between batches, and mixing lots leaves a visible patch. Before ordering, check what is underneath. Tile fails at the substrate rather than the surface, and deflection in a floor cracks both tile and grout. On a wood subfloor that means cement board or an uncoupling membrane, and in a shower it means a proper tile backer — moisture-resistant drywall is not a wet-area substrate.

Worked example

A 10 × 12 ft floor in 12 × 24 in tile, straight lay

1Area: 10 × 12 = 120 ft²
2Add 10% waste: 120 × 1.10 = 132 ft²
3Each tile covers 2 ft², so 132 ÷ 2 = 66 tiles
4At 8 tiles per box: 66 ÷ 8 = 8.25 boxes

Order 9 boxes, all from the same shade lot.

Run your own numbers below — the Tile Calculator handles the unit conversions and waste factor for you.

Tile Calculator

Calculate tiles, boxes, and cost for floors, walls, backsplashes. Configurable tile size, box quantity, and waste percentage.

Formula and figures last reviewed August 6, 2026 — Cosyslabs · how we verify

Inputs

Area to cover(ft²)

Tile size

Waste %

Tiles per box

Price per box (optional)($)

Result

Tiles

132

Boxes

Coverage

120 ft²

Tile size: 12"
Waste: 10%

Waste default: 10% — TCNA Handbook recommends 10% waste for standard layouts, 15% for diagonal.

Diagram

Estimates only. Verify with a licensed contractor or supplier before purchasing. Rough Estimator! is not responsible for shortages, overages, or material variances. See our methodology for formulas and sources.

Formula

Tiles = ceil(area × (1 + waste) ÷ tile area)

References

Measure what the tool asks for
This calculator works from area to cover in ft² and price per box (optional) in $. Measure the finished area you are covering, not the material — an estimate is only as good as the dimensions you feed it.
What it does with those numbers
Tiles = ceil(area × (1 + waste) ÷ tile area) Every figure on the page comes out of that one expression, so you can check it by hand.
Why it adds 10% waste
TCNA Handbook recommends 10% waste for standard layouts, 15% for diagonal.
Choosing a tile size
Pro tip: Larger tiles (18"+) make small rooms feel bigger and have fewer grout joints to clean, but require a flatter substrate.
Where the numbers come from
The constants are taken from TCNA Handbook for Ceramic, Glass, and Stone Tile Installation, ANSI A108/A118/A136 — American National Standards for tile installation and ASTM C627 — Evaluating Ceramic Floor Tile Installation Systems, linked in full below. If a figure here disagrees with your supplier's spec sheet, use the spec sheet — it describes the product you are buying.
What this will not tell you
This is a material takeoff, not a bid. It does not price labour, permits, delivery, equipment hire or site preparation, and it assumes a straightforward layout. Complex cuts, difficult access and awkward shapes all cost more than the geometry suggests.

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Backer board
Sealer

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Frequently asked questions

10% for standard installations, 15% for diagonal layouts, 20% for complex patterns.

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Cite this page

Cosyslabs. (2026). Tile Calculator. Rough Estimator!. https://roughestimator.com/tile-calculator

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