DIY Cost Tools
Trapezoid Area Calculator
MATH CALCULATOR
Calculate trapezoid area from two parallel sides and their perpendicular separation.
Use consistent units. All fields are required; absolute input values must not exceed one trillion. The two entered sides must be parallel.
How to use this calculator
Replace the example inputs with your measurements, then select Calculate. Results use the units shown beside each field. Keep extra precision in the inputs and round only when recording the final answer.
Formula and explanation
Area = (first base + second base) × height ÷ 2
The area equals the average length of the parallel sides multiplied by their perpendicular separation.
Worked example
With First parallel side (units) = 8, Second parallel side (units) = 12, Perpendicular height (units) = 5, the results are Area (square units): 50; Average base length (units): 10.
Important limitations
The two entered sides must be parallel. A sloping edge is not the height. This tool does not determine perimeter from three measurements.
Results are estimates based on the entered values. Numeric precision does not eliminate measurement uncertainty.
Frequently asked questions
Can I swap the two bases?
Yes. Their sum is the same in either order.
What units should I use?
Use the same length unit for all three inputs. The result uses the corresponding square unit.
What happens if I leave a field blank?
The tool clears the previous result and asks for valid inputs, so an old answer is not mistaken for a new calculation.
Review notes
Reviewed October 1, 2026. Default calculations were checked independently against the displayed equations. The script validates blank, nonfinite, out-of-range, and formula-specific invalid inputs. Calculations run locally in your browser.