Room Size Cheat Sheet
A one-page reference for ten common room dimensions — square feet, square meters, carpet yards, flooring to buy, perimeter, corner-to-corner diagonal, and two-coat paint gallons. Every column is computed from the two numbers in the first column, so you can check any cell with a calculator.
Last updated:Room Size Cheat Sheet — FootyCalc.com
| Room (ft) | Sq ft | Sq m | Sq yd | Floor +10% | Perim (ft) | Diag (ft) | Paint 2 coats | Typical use |
|---|---|---|---|---|---|---|---|---|
| 8 × 8 | 64 | 5.95 | 7.1 | 71 sq ft | 32 | 11.31 | 2 gal | Half bath, closet |
| 8 × 10 | 80 | 7.43 | 8.9 | 88 sq ft | 36 | 12.81 | 2 gal | Small office |
| 10 × 10 | 100 | 9.29 | 11.1 | 111 sq ft | 40 | 14.14 | 2 gal | Bedroom, office |
| 10 × 12 | 120 | 11.15 | 13.3 | 132 sq ft | 44 | 15.62 | 2 gal | Standard bedroom |
| 12 × 12 | 144 | 13.38 | 16.0 | 159 sq ft | 48 | 16.97 | 2 gal | Dining, guest room |
| 12 × 15 | 180 | 16.72 | 20.0 | 199 sq ft | 54 | 19.21 | 3 gal | Primary bedroom |
| 14 × 16 | 224 | 20.81 | 24.9 | 247 sq ft | 60 | 21.26 | 3 gal | Living room |
| 15 × 20 | 300 | 27.87 | 33.3 | 330 sq ft | 70 | 25.00 | 3 gal | Large living room |
| 16 × 20 | 320 | 29.73 | 35.6 | 352 sq ft | 72 | 25.61 | 3 gal | Primary suite |
| 20 × 20 | 400 | 37.16 | 44.4 | 441 sq ft | 80 | 28.28 | 4 gal | Garage, great room |
How Every Cell Is Calculated
Nothing in the table is looked up or rounded from somebody else's estimate. Seven formulas produce all of it:
- Sq ft = width × length. 12 × 15 = 180.
- Sq m = sq ft × 0.09290304. The factor is exact (NIST SP 811, Appendix B.8), so 180 sq ft = 16.72 m², not "about 17".
- Sq yd = sq ft ÷ 9. Carpet is sold by the square yard, and a 12 × 15 floor is 20.0 sq yd before any seam allowance.
- Floor +10% = ceil(sq ft × 1.10), rounded up to a whole square foot because you cannot buy a partial plank. Straight-lay waste; a diagonal layout is 15% and herringbone or chevron 15–22%.
- Perim = 2 × (width + length). Deduct 3 ft per door opening to get baseboard: a 12 × 15 room has 54 ft of wall line and 51 ft of baseboard plus one door casing.
- Diag = √(width² + length²), the longest rigid item that can lie flat on the floor corner to corner — useful for a board, mattress, or sofa that will not go in straight along a wall.
- Paint 2 coats = ceil((perim × 8 ft ceiling − 21 sq ft door − 30 sq ft of two windows) × 2 ÷ 350). The 350 sq ft per gallon figure is an assumption, not a standard — read the coverage on the can you actually buy, and note the ceiling is a separate 180 sq ft at this size.
One row fails the building-code floor. A published 2018 IRC adoption sets a habitable room at no less than 70 sq ft with no horizontal dimension under 7 ft (kitchens excepted): 8 × 8 = 64 sq ft is 6 sq ft below that, so it works as a half bath, closet, or laundry but not as a bedroom. Every other row clears both tests, and all ten have a short side of at least 8 ft against the 7 ft minimum. States and municipalities amend these clauses individually, so confirm the text your jurisdiction adopted before designing to the minimum.
How to Use This Sheet
- Click Print / Save as PDF above — the sheet prints as one page with the navigation and related-tool cards removed.
- Need a size that is not here? All 61 room-size pages run the same formulas for dimensions from 8 × 8 to 50 × 100 ft, or enter anything in the room calculator.
- Comparing two footprints of the same area — 12 × 20 and 15 × 16 are both 240 sq ft — read the perimeter and diagonal columns, not the square footage.
Sources
- Square foot → square meter (0.09290304) and foot → meter (0.3048), both exact — nist.gov — SP 811 Appendix B.8.
- Habitable-room minimums (70 sq ft floor area, 7 ft horizontal dimension, kitchens excepted) — 2018 IRC Section R304 as published in a municipal adoption document: bullheadcityaz.gov — 2018 IRC attachment.
- Waste allowance by laying pattern (5–10% straight, 15% diagonal, 15–22% herringbone or chevron) — trade guidance, not a code requirement: tilecalculators.com — tile waste by pattern.
US room sizes in context — median new-home area, bedroom counts, and why no federal series measures an individual room — are in our Average Room Sizes in American Homes (2026) report. The 350 sq ft per gallon paint coverage is the only figure on this sheet we could not source to a published standard, so it is labeled as an assumption in the formula above. All sources were fetched on ; outbound links carry rel="nofollow" because citing a source is not the same as endorsing a page.