Trapezoid Area Calculator
Average the two parallel sides to get the mean width, then multiply by the height. The second figure is that mean width.
Your numbers
Area
40cm²
Result
8cm
Formula
Area = (Top edge + Base) × Height ÷ 2
Height is the perpendicular distance between the parallel sides, not the length of a slanted side.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Top edge (cm)The shorter parallel side of a trapezium. | 6 | 0 and up |
| Base (cm)The side you treat as the bottom when finding area. | 10 | 0 and up |
| Height (cm)The perpendicular height from the base — not the slanted side. | 5 | 0 and up |
Step by step
Quick reference table
Results when only Top edge (cm) changes and everything else stays put.
| Top edge (cm) | Area (cm²) | Result (cm) |
|---|---|---|
| 3 | 32.5 | 6.5 |
| 4.5 | 36.25 | 7.25 |
| 6 | 40 | 8 |
| 9 | 47.5 | 9.5 |
| 12 | 55 | 11 |
What each result means
| Result | At default values |
|---|---|
| Area (cm²)The space a shape covers — length squared. | 40 |
| Result (cm)What the formula gives back — the answer this page is for. | 8 |
Common mistakes
Height is the perpendicular distance between the parallel sides, not the length of a slanted side.
Glossary
- Top edge
- The shorter parallel side of a trapezium.
- Base
- The side you treat as the bottom when finding area.
- Height
- The perpendicular height from the base — not the slanted side.
- Area
- The space a shape covers — length squared.
- Result
- What the formula gives back — the answer this page is for.
Frequently asked questions
Q. How is Trapezoid Area Calculator calculated?
Area = (Top edge + Base) × Height ÷ 2 — Average the two parallel sides to get the mean width, then multiply by the height. The second figure is that mean width.
Q. Can you walk through an example?
With Top edge 6cm, Base 10cm, Height 5cm, the answer is Area 40cm².
Q. What do I need to enter?
Enter Top edge, Base, Height. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Top edge (cm) moves the answer to Top edge (cm) 3 → Area (cm²) 32.5 and Top edge (cm) 12 → Area (cm²) 55. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Height is the perpendicular distance between the parallel sides, not the length of a slanted side.
Related calculators
Keep your length units consistent across inputs — mixing centimetres and metres throws results far off.