Guide · 6 min read
How to Measure a Room for Tile (Step by Step)
Measure any room for floor or wall tile: handle closets and alcoves, convert inches to decimals, subtract fixtures, and add the right waste percentage.
Free calculator — runs in your browser, nothing is uploaded.
Start with the big rectangle
Every room is a collection of rectangles. Measure the main space first: wall to wall, in feet and inches. Write both dimensions down before you measure anything else — most measuring mistakes come from holding numbers in your head.
Convert the inches to decimals before multiplying: 10 ft 6 in becomes 10.5 ft, 12 ft 3 in becomes 12.25 ft. Multiplying 10.5 × 12.25 gives you 128.6 sq ft — the number every tile box and calculator works in.
Handle alcoves, closets and bump-outs
Measure each alcove or closet separately as its own rectangle and add it to the main area. A 3 × 4 ft closet adds 12 sq ft — enough that forgetting it can leave you a box short on a mid-sized room.
Bump-outs like a fireplace hearth or a cabinet footprint work in reverse: measure them and subtract. Only subtract permanent fixtures that will not be tiled under — kitchen islands on the finished floor, tubs, and built-in vanities.
Tools that make measuring easier
DGSL Tile Leveling System with Plier, 300 Tile Spacers 1/16" and 100 Wedges
$25.99
Check price on Amazon
As an Amazon Associate I earn from qualifying purchases.
Prices as of Oct 10, 2026, 6:33 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
Walls: doors and windows
For wall tile, measure each wall separately: width times height. Subtract doors and windows by their rough opening size — a standard door is about 21 sq ft, a typical window 6–12 sq ft.
Don't subtract anything smaller than about 2 sq ft (outlets, niches you'll tile inside, pipe penetrations). The tile you lose cutting around them roughly equals what you'd have ordered anyway.
Add waste — and write the number on the wall
Straight layouts need 10% extra for cuts and breakage; diagonal and herringbone patterns need 15–20%. Multiply your net area by the waste factor, and that final number is what you order.
Pro habit: write each wall and floor dimension in pencil directly on the surface. When you're knee-deep in thinset two days later wondering about the far wall, the answer is on the wall.
- Main rectangle: length × width (inches converted to decimals)
- Add alcoves and closets; subtract permanent fixtures only
- Walls: subtract doors and windows over ~2 sq ft
- Add 10% waste for straight layouts, 15–20% for patterns
Do this math on the job site — in the free app
Smart Tile Calculator for Android: offline, in your pocket, free.
FAQ
How do I convert inches to decimal feet?
Divide the inches by 12. 6 in = 0.5 ft, 3 in = 0.25 ft, 9 in = 0.75 ft. So 12 ft 3 in is 12.25 ft.
Should I measure under the toilet or vanity?
For floors, measure the full footprint — you'll tile under the toilet flange area. Subtract only fixtures that sit on the finished floor permanently, like a vanity or island.
How accurate do measurements need to be?
To the nearest inch is fine. The 10% waste allowance absorbs small measuring errors — precision matters more for layout planning than for ordering.
Keep reading
- Choosing the Right Tile Size for Your Room
How tile size changes a room: when 12×24 beats 4×4, why small rooms can take large tile, grout line math, and the flatness rule for big formats.
- How Many Tiles Do I Need? A Worked Example, Start to Finish
A real 10×12 room taken from tape measure to order quantity: net area, waste factor, per-tile coverage, box math, and the attic stock rule.