How to measure a room for flooring
To measure a room for flooring, multiply its length by its width to get the square footage, then add about 10% for waste. A 12 × 15 ft room is 180 sq ft — roughly 198 sq ft once you include waste. Here's how to do it accurately, even in tricky rooms, and how to turn the number into boxes you can actually order.
What you'll need
- A tape measure (a laser measure is faster for big rooms)
- Paper or your phone to jot down numbers — a rough sketch of the room helps more than you'd think
- A calculator — or ours, linked below
Step 1: Measure length and width
Measure the room at its longest and widest points, in feet. If the baseboards are off, measure wall to wall at floor level. Rooms are rarely perfectly square, so take each measurement in two places and use the larger number. Write both down.
Step 2: Multiply for square footage
Length × width = area in square feet. A 12 × 15 ft room is 180 sq ft. This is the bare floor area before any waste. (Working in inches or meters? The square footage calculator converts as it sums.)
Step 3: Handle odd-shaped rooms — a worked example
For L-shaped rooms or spaces with alcoves, split the floor into rectangles, measure each one, and add the areas together:
- Main area: 16 × 12 = 192 sq ft
- Alcove: 6 × 4 = 24 sq ft
- Total: 192 + 24 = 216 sq ft → with 10% waste, order ~240 sq ft
Sanity-check the split: the pieces' dimensions should add back up to the overall wall lengths. For a bay window or angled nook, measure the largest rectangle that contains it — the extra becomes part of your waste buffer.
Step 4: Count the spaces people forget
- Closets: each is its own small rectangle — a 2 × 6 ft reach-in adds 12 sq ft, and a walk-in can add 30+.
- Doorways and transitions: flooring runs to the center of each doorway; measure to there, and note each threshold — transition strips are sold separately.
- Stairs: figure about 5 sq ft per step for a standard 3.5-ft-wide staircase (a ~10 in tread plus ~7.5 in riser), so a 13-step flight is ~65 sq ft, plus stair-nose trim per step.
- Under appliances and furniture: if the fridge or a built-in sits on the new floor, its footprint counts.
Step 5: Add a waste allowance
Always buy more than the exact area to cover cuts, mistakes, and future repairs.
| Layout | Add for waste |
|---|---|
| Straight, simple room | 8–10% |
| Rooms with many cuts or angles | 10–15% |
| Diagonal layout | 15% |
| Herringbone or chevron | 15–20% |
Plank direction nudges this too: planks usually run parallel to the longest wall or the main light, and a direction that forces lots of short end-cuts eats a little more of the allowance.
Let the calculator do steps 2–6
Enter your measurements and box size into our flooring calculator to get the square footage, waste, number of boxes, and cost in one go.
Open the Flooring CalculatorStep 6: Convert to boxes
Flooring is sold by the box, and coverage per box varies by product — roughly 18–24 sq ft is common for laminate and vinyl planks. Divide your total square footage (including waste) by the coverage printed on the carton, then round up: the 240 sq ft L-shaped room above needs 12 boxes at 20 sq ft per box. Buy one extra box and keep it — if the line is discontinued later, you'll have a perfect-match repair on hand from the same dye lot.
Carpet plays by different rules
Broadloom carpet comes on 12-ft rolls (sometimes 13.5 or 15 ft), so you pay for the cut, not the room's area. A 10 × 13 ft room needs a 12 × 13 cut — 156 sq ft even though the room is 130 — and a room wider than the roll needs a seam, placed away from traffic and light. Patterned carpet adds pattern-repeat waste on top. This is why carpet quotes come from the installer's seam diagram, not a simple length × width; use your room's raw square footage for budgeting and let the shop confirm the cut.
Common mistakes to avoid
- Forgetting waste. Ordering the exact area almost always leaves you short.
- Skipping closets and stairs. They're small individually and a full box or two together.
- Mixing dye lots. Buy it all at once so planks match.
- Ignoring transitions and trim. Doorway trims, thresholds, and quarter-round are sold separately — measure the room's perimeter for trim while the tape is out.
- Measuring over old flooring you'll remove. Thick carpet and pad can hide a jog in the wall; measure the bare floor where you can.