Find a room floor area and perimeter at once. Enter the room size to get square footage for flooring and linear feet for baseboard or trim.
Usage Tip
Sketch the room and note each wall length. The perimeter here is the full loop — subtract about 3 ft for each doorway when buying baseboard.
Perimeter = 2 × (Length + Width)
Totals = per-room values × number of rooms
This assumes rectangular rooms; break an L-shape into rectangles and total them.
Subtract door openings from the perimeter for baseboard (roughly 3 ft per standard door), and skip walls where trim is not run.
For flooring the floor area is what matters; for paint you want wall area instead (perimeter times wall height).
How to Calculate Room Area
For a plain rectangular room, multiply length by width: a 12 by 16 ft room is 192 square feet. For square rooms, multiply the side by itself. For L- and U-shaped rooms, split the floor into rectangles, find each area, and add them up – or use the shape presets above, which do the splitting for you.
Common Room Sizes
| Room | Typical size |
|---|---|
| Bedroom | 120-200 sq ft |
| Living room | 200-400 sq ft |
| Kitchen | 100-250 sq ft |
| Bathroom | 35-100 sq ft |
| Dining room | 120-200 sq ft |
And a quick area reference for common dimensions:
| Room size | Area |
|---|---|
| 10 × 10 | 100 sq ft |
| 12 × 12 | 144 sq ft |
| 12 × 16 | 192 sq ft |
| 15 × 20 | 300 sq ft |
Flooring Estimation Guide
Flooring is sold by the square foot, often in cartons that cover a set area (laminate and vinyl plank around 20 sq ft per box; tile varies). Take the room area, add 10% waste for cuts, then divide by the carton coverage and round up. Example: a 192 sq ft room plus 10% is about 211 sq ft; at 20 sq ft per carton that is 11 cartons. Set the calculator to Flooring and it returns the carton count.
Paint Estimation Guide
Paint covers walls, not floor, so it is based on wall area – the room perimeter times the ceiling height, times the number of coats. One gallon covers roughly 350 sq ft per coat. Example: a 12 by 16 ft room has a 56 ft perimeter; at 8 ft ceilings that is 448 sq ft of wall, or about 2 gallons for two coats. Subtract a little for large doors and windows. Set the calculator to Paint and enter your ceiling height.
Carpet Estimation Guide
Carpet is usually sold by the square yard (1 sq yd = 9 sq ft) and comes in 12 ft wide rolls, so real-world waste runs higher than for flooring. Take the area, add 10% (more for rooms wider than 12 ft or with odd shapes), and divide by 9 for square yards. Example: 300 sq ft plus 10% is 330 sq ft, about 37 sq yd. Set the calculator to Carpet for the square-yard figure.
Measuring Irregular Rooms
Break any odd shape into rectangles. For an L-shaped room, treat it as a large rectangle with a corner removed, or as two rectangles side by side. For a U-shape, three rectangles. Measure each section, add the areas, and remember to include closets and alcoves if they will be floored, and to subtract islands or fixed cabinets that will not. Bay windows and angled walls are usually close enough if you box them to their widest points.
Waste Factor Recommendations
| Material | Suggested waste |
|---|---|
| Laminate / vinyl plank | 10% |
| Tile | 10-15% |
| Hardwood | 10% |
| Carpet | 10% (more if room > 12 ft wide) |
| Paint | 5-10% |
Add toward the higher end for diagonal layouts, busy patterns, or lots of corners and closets.
Remodeling Planning Tips
- Measure every room you plan to touch and total the areas before ordering.
- Order all flooring of one batch / dye-lot at once to avoid shade mismatch.
- Keep 5-10% as attic stock for future repairs.
- Account for transitions, thresholds, and underlayment separately.
- Sketch the layout and label each measurement so nothing gets double-counted.
Common Measuring Mistakes
- Measuring wall-to-wall but forgetting closets and alcoves.
- Using floor area for paint instead of wall area.
- Skipping the waste allowance and coming up short.
- Forgetting that carpet and flooring come in fixed widths and cartons.
- Rounding dimensions down instead of up.
Frequently Asked Questions
How do I calculate the area of a room?
Multiply length by width for a rectangular room. For L- or U-shaped rooms, split into rectangles, find each area, and add them together.
How much flooring do I need for my room?
Take the room area, add about 10% for waste, then divide by the coverage of one carton and round up. The Flooring mode above does this automatically.
How much paint do I need?
Paint is based on wall area: perimeter times ceiling height times coats, divided by about 350 sq ft per gallon. Use the Paint mode and enter your ceiling height.
How do I measure an L-shaped room?
Split it into two rectangles (or a bounding rectangle minus the missing corner), calculate each area, and add. The L-shaped preset handles the math for you.
How much extra should I buy for waste?
About 10% for most flooring, 10-15% for tile, and a bit more for carpet in wide or oddly shaped rooms.
Do I include closets in the room area?
Yes, if you are flooring them. Add closet and alcove areas; subtract anything fixed in place that will not be covered.
Related Area Calculators
Note: results are planning estimates. Material coverage, carton sizes, and roll widths vary by product, and waste depends on layout, pattern, and room shape – always confirm against the product label and add a waste allowance. Include closets and alcoves you will cover and subtract fixed obstructions. Irregular and angled rooms are approximated by boxing to rectangles. General DIY guidance, not a professional estimate.