Tile calculator

How many tiles for the floor or wall, with the waste factor set by the pattern you're laying instead of a flat 10%. A herringbone job throws away twice what a straight grid does, and the calculator that ignores that leaves you a box short.

01 How the math works

Tile is a coverage problem with two twists. Work out the surface area, divide by the area one tile covers, then add a waste factor for the cuts and breakage. The first twist is that a tile covers slightly more than its nominal size once you count the grout joint. The second is that the waste factor isn't one number — it depends on how you're laying the tile.

The grout joint gets added to each tile dimension because the joint is part of what a tile "covers" on the wall. A 12 in tile with a 1/8 in joint occupies 1.02 ft², not 1.00. On a 12-inch tile that shaves the count by roughly one tile per 50; on a 2 in mosaic the joint is a real slice of the surface, and skipping it over-counts the order.

The waste factor is where most calculators stop thinking. They apply a flat 10% to every job. The TCNA figure is 10% only for a simple rectangular room laid straight — a diagonal layout runs 15% because every edge tile is a two-cut triangle, and herringbone or mosaic runs 20% because the offcuts rarely fit anywhere else.

02 Worked example

Take a 6 ft × 8 ft bathroom floor (1.83 m × 2.44 m) in 12×12 in tile (305×305 mm) with 1/8 in grout joints (3 mm), laid straight. The area is 48 ft² (4.46 m²). At the TCNA straight-layout waste of 10%, that's 53 ft² (4.92 m²) of tile to buy for.

Now the count. With the joint added, one tile covers 1.02 ft², so the floor takes 48 ÷ 1.02 = 47 tiles before waste, and 47 × 1.10 = 52 tiles rounded up. The naive rule — one 12-inch tile per square foot — gives 53. One tile's difference here, because the tile is large. Swap in a small mosaic and that gap widens fast.

Change only the layout and the order moves more. The same floor in herringbone carries a 20% waste factor: 47 × 1.20 = 57 tiles. Five tiles more than the straight version, on an identical floor, purely because of the cutting pattern. For thinset, the floor's actual 48 ft² at the low-end coverage of 80 ft² per 50 lb bag needs a single bag.

03 When this calculator is wrong

The flat 10% waste factor most calculators use is calibrated for production-scale work on a plain rectangular room laid straight. On a small floor with a busy pattern, real waste runs 15–20%, because the offcuts from a diagonal or herringbone cut usually can't be reused — the angle is wrong for the next spot. Match the waste setting to the layout and the tile you can't reuse is already in the count. Buying a straight-layout 10% and then laying herringbone is how a job ends one box short.

• Layout waste is not breakage or attic stock. The 10/15/20 covers cutting waste, not the tiles that snap on the wet saw or the reserve you keep for future repairs. Add a box, or about 5%, on top for a dye-lot match — once a tile lot is exhausted the replacement comes back a shade off, and a patched repair reads as a patch.
• It assumes a rectangle. The calculator takes one length and one width. An L-shaped room, a floor with a kitchen island, or a wall broken up by a window and a door needs to be split into rectangles and added — feed each piece in and total the tiles yourself.
• The grout-joint effect is small on big tiles and large on mosaics. On a 12 in tile a 1/8 in joint changes the footprint by about 2%. On a 2 in mosaic the same joint is a much bigger share of each tile, so getting the joint width right matters far more there.
• Rectified and non-rectified tiles use different joints. Rectified tile is ground to an exact size and takes joints as tight as 1/16 in (1.6 mm); pressed tile with a cushioned edge needs a wider joint. Set the joint to what you'll actually grout, not what looks tidiest.

04 What to do with the result

Order the rounded-up tile count, then round again to whole boxes — tile is sold by the box, and a box you open for two tiles still counts as bought. Match the pattern setting to what you're laying before you read the number: the difference between straight and herringbone on the bathroom floor above is five tiles, which is most of a box.

Buy the full order in one trip, from one lot. Tile is fired in batches and colour drifts between them, so a second order weeks later can arrive close but not matching — enough to catch the eye on the same floor in daylight. That's the argument for the extra box of attic stock: it's cheaper to store a few spare tiles than to re-tile a patch when the lot is gone.

05 Common questions

How many tiles do I need per square foot?

Divide the area by what one tile covers, including its grout joint. A 12×12 in tile with a 1/8 in joint covers 1.02 ft², so a 48 ft² floor takes about 47 tiles before waste. Then add the waste factor for your layout.

How much extra tile should I buy for waste?

10% for a rectangular room laid straight, 15% for a diagonal or offset layout, and 20% for herringbone or mosaic — the TCNA Handbook figures. Add another box or about 5% on top for breakage and a dye-lot repair reserve.

Does the grout joint change how many tiles I need?

Yes, and it lowers the count. A tile plus its joint covers more wall than the tile alone, so you need slightly fewer full tiles. The effect is about 2% on a 12 in tile and much larger on small mosaic, where the joint is a real share of each piece.

How much thinset do I need?

Thinset covers the substrate, so it scales with the actual area, not the waste-inflated tile count. A 1/4 × 3/8 in notched trowel spreads a 50 lb bag over 80–100 ft² — so a 48 ft² floor is one bag. Larger tiles and a deeper notch use it faster.

How do I figure tiles for a diagonal or herringbone layout?

Same area, higher waste. Set the pattern to diagonal for 15% or herringbone for 20% and the calculator raises the count. The extra tiles cover the edge cuts, which multiply when tiles meet the wall at an angle instead of square.