TileQuantCoverage math for tile, thinset and grout — before you buy.

How many 18″ tiles for a 10 × 20 ft room?

18" tiles needed
98tiles
220 ft² of tile for a 10 × 20 ft room
Plan10 ft20 ft9818″ tiles220 ft² to buy5 bags thinset1/2" × 1/2" square-notch
Floor area200ft²
Buy for+10% cuts and breakage220ft²
18" × 18" tiles98tiles
Thinset (50 lb bags)45 ft² per bag with a 1/2" × 1/2" square-notch5bags
Grout (0.125" joints)1 × 25 lb bags13.2lb

Notes

  • Thinset coverage is set by trowel size, not by room size — a 18" tile needs a 1/2" × 1/2" square-notch, so a 50 lb bag covers about 45 ft².
  • Add 15% instead of 10% for a diagonal layout, a room with many jogs, or if the tile has a pattern that has to line up.
  • Grout is figured at 0.125" joints and 0.5" tile thickness. Wider joints raise it quickly.

Tiles, and then some

The floor is 200 ft². Buying exactly that much is how people end up back at the store: cuts at the walls, the odd broken tile and a spare box for future repairs mean you order 220 ft² — 10% over.

At 18″ square that works out to 98 tiles.

Thinset depends on the tile, not the room

This is where rule-of-thumb estimates go wrong. A bigger tile needs a bigger notched trowel, and a bigger notch puts down more mortar per square foot. For 18″ tile you want a 1/2" × 1/2" square-notch, which is why the bag count here is 5 rather than whatever a generic calculator returns.

Before you order

Measure the room at more than one point. Rooms are rarely square, and the widest measurement is the one that decides how many tiles the last row needs.

Nearby sizes

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