How do I work out the area of a room?
Multiply the length by the width, both in the same unit. A room 4 m by 3 m is 12 m². In feet, a room 12 ft by 10 ft is 120 square feet, which is 11.15 m².
Area Calculator
The area of any shape, in the units you order in, with the extra for waste.
Your answer
The area of your space
Choose a shape and type its measurements, and the area appears here with the working and a drawing to scale.
The working
Rectangle: area = length × width
length = 4, width = 3 → area = 12 m² = 12 × 1 = 12 m². Plus 10%: × 1.1 = 13.2 m².
| Shape | Area |
|---|---|
| Rectangle | length × width |
| Square | side × side |
| Triangle | base × height ÷ 2 |
| Circle | π × radius² |
| Semicircle | π × radius² ÷ 2 |
| Trapezoid | (top + bottom) ÷ 2 × height |
| Parallelogram | base × height |
| Ellipse (oval) | π × half-length × half-width |
| Sector (slice) | π × radius² × angle ÷ 360 |
| Ring (annulus) | π × (outer² − inner²) |
| Regular polygon | n × side² ÷ (4 × tan(180° ÷ n)) |
Worked examples
- A room 4 m × 3 m: 12 m²; with 10% extra, 13.2 m². At 1.86 m² a box that is 8 boxes.
- An L-shaped room, 5 m × 4 m plus 3 m × 2 m: 20 + 6 = 26 m².
- A round patio 3 m in radius: π × 3² = 28.27 m². A trapezoid bed 4 m and 8 m wide, 5 m deep: (4 + 8) ÷ 2 × 5 = 30 m².
Good to know
Measuring for real jobs
- Split odd shapes. L-shaped rooms, gardens with curved beds, and walls with windows are just simple shapes added up and cut-outs taken away.
- Squared units trip people up. 1 m is 3.28 ft, but 1 m² is 10.76 ft². Convert the final area, not one side in your head.
- Keep waste separate. Write down the true area and the extra you add, so a quote can be checked later.
- Radius, not diameter. Circle formulas use the radius: half the width across.
- Don't mix units on the same shape, and don't confuse area with the distance around (perimeter).
Questions
Questions people ask about area
What if the room is not a rectangle?
Split it into rectangles and other simple shapes, work out each one, and add them up; take away any cut-outs. An L-shaped room made of 5 m × 4 m and 3 m × 2 m is 20 + 6 = 26 m². The Combine tab keeps the running total.
Why is area in square units?
Area counts two directions at once. A 2 ft by 3 ft panel covers 6 square feet, not 6 feet. Because both sides change when you change units, 1 m² is 10.76 square feet, not 3.28.
How much extra should I allow for waste?
Keep the measured area and the extra separate. Flooring and tiles often need about 5–15% for cuts and breakage; check the product's own advice. 12 m² plus 10% is 13.2 m² to buy.
How many boxes or packs do I need?
Divide the area to buy by the coverage on one pack, then round up. 13.2 m² of flooring at 1.86 m² a box is 7.1, so you need 8 boxes. The Order tab does this, with the cost.
How big is an acre or a hectare?
A hectare is 10,000 m², a square 100 m a side. An acre is 4,046.86 m², about 40% of a hectare; one hectare is about 2.47 acres.
Printout
Your measurement sheet
One page for a quote or a trip to the shop: the shape and its sizes, the area in every unit, the extra, the packs and the cost, with room for notes.
For spreadsheets and code
Check it yourself
import math
# Rectangle, in m
length = 4
width = 3
area = length * width
print(f"{area:.4f} m2, with 10% extra {area * 1.1:.4f}")Both print 12 m2 for your rectangle.
Area measurement sheet
Job: ______________________ Date: 2 November 2026
| Shape | Rectangle: length × width |
|---|---|
| Sizes | Length 4 m, Width 3 m |
| Area | 12 m² = 129.17 ft² = 14.35 yd² |
| Extra | 10% → 13.2 m² to buy |
| Packs | 8 × 1.86 m² = $360.00 |
| Land | 0.002965 acres, 0.0012 ha |
Rectangle l × w · triangle b × h ÷ 2 · circle π r² · trapezoid (a + b) ÷ 2 × h · 1 m² = 10.764 ft² · 1 acre = 4,046.86 m² · 1 ha = 10,000 m²
Notes: ____________________________________________________________
Straight, square edges; one unit for every side. calculationtime.com/calculators/area-calculator/
Sources
Where the formulas and factors come from
Printables
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