Floor tile calculator

How the number is worked out

Floor area divided by the area one tile occupies. That second figure is the module: the tile's measured size plus one grout joint in each direction, not the size on the label.

This trips people up in both directions. A tile sold as "12 × 12" usually measures about 11-7/8 in, and with a 1/8 in joint the module comes back to a clean 12 in — so 100 sq ft really is 100 tiles. But a tile that measures a true 12 in with a 1/8 in joint occupies 12.125 × 12.125 = 1.02 sq ft, and 100 sq ft only takes 98 of them. Measure the tile before you order, and only fill in the grout joint box above if your tile is full size.

Waste is set by the layout, not by a rule of thumb

A flat 10%, applied to every job, is the usual rule of thumb. The geometry says otherwise, which is why the layout above changes the figure. On a straight grid the cuts along the walls are rectangles, and a rectangle off-cut from one wall often fits the opposite wall. Turn the field 45° and every perimeter cut is a triangle — two triangles from one tile only ever fit if the wall happens to be the right length, so most of them are scrap. In herringbone, each course ends on a diagonal and the pattern has to restart, so the loss is higher again.

Be clear about what these numbers are: no standard publishes a waste percentage per layout. Manufacturers stay general — MSI says to order "an additional 5% to 10%" — and the per-pattern figures above are what tile setters actually order. They are a starting point you should raise, not lower, if the room is complicated. Large format is its own surcharge: a broken 12 × 24 costs you twice the tile a broken 12 × 12 does, and Marazzi requires medium-bed mortar and a minimum 3/16 in joint above 20 in, which means less tolerance everywhere.

Buy every box at once

Ceramic and porcelain are fired in batches, and the shade of a batch drifts. Manufacturers do not treat this as a defect — Marazzi's own installation sheet says "variation of shades is an inherent characteristic of ceramic tile" and tells you to mix tiles from several cartons as you set so the variation averages out across the floor.

The practical consequence: the box you go back for in three weeks will be a different shade lot, and one box of it laid in a corner will read as a patch forever. Buy the spare box with the original order, check the shade and calibre codes printed on every carton match before you open any of them, and keep the leftovers — a cracked tile in year five is unfixable otherwise.

Thin-set

The bag count is driven by the trowel, not the tile. CUSTOM Building Products publishes 85–95 sq ft per 50 lb bag with a 1/4 × 1/4 square-notch and 42–47 sq ft with a 1/2 × 1/2 — the same floor takes twice the mortar when you step up a notch size. This calculator uses the low end of each range.

What the waste factor cannot see

Everything on this page is area arithmetic. The floor is length × width, the layout picks a percentage, and the percentage is applied to the area. No tile is ever laid out, and that is the limit worth knowing, because cutting loss is not really a property of area — it is a property of how your room divides by your tile.

Two 100 sq ft rooms make the point. A 10 × 10 room in 12 in tile has ten whole tiles in each direction and no cuts at all, so the allowance is 10% of nothing. A room measuring 10 ft 4 in by 9 ft 8 in is the same area and needs a rip on every course in both directions — a 4 in strip along one wall, an 8 in strip along the other — and those only fit anywhere else if the opposite wall wants the identical width. The page gives both rooms the same percentage. Small rooms make this worse rather than better: 10% of a 35 sq ft bathroom is three and a half square feet, and a bathroom can spend that cutting round the toilet flange alone.

Also outside the estimate:

• The room is a rectangle. No field exists for an alcove, an island, a hearth or a fireplace return. Break the floor into rectangles and add them.
• Trim is not counted. Bullnose, base tile, thresholds, stair nosings and the tile wrapping a shower curb are bought by the piece or the linear foot, and none of them are in any number here.
• The mortar follows the floor, not the order. Bag count is the bare tiled area at the low end of CUSTOM's published range, with nothing added for what stiffens in the bucket, for a substrate that needs flattening first, or for back-buttering a large-format tile.
• Tiles and boxes are worked out separately from the same order area, so they will not agree exactly. Buy to the box count — the tile count is there to sanity-check it against the carton.