Triangle Area Calculator
Calculate triangle area from base and perpendicular height or from three side lengths. Mix regional units and follow the area formula with a diagram.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
For a known perpendicular height, area = base × height ÷ 2. For three sides, compute the semiperimeter s = (a + b + c)/2 and use Heron’s formula. The three sides must satisfy the triangle inequality.
A = bh/2; or A = √[s(s − a)(s − b)(s − c)]
Worked example
A base of 3 m with perpendicular height 4 m gives 6 m². Separately, sides 3 m, 4 m and 5 m also give 6 m² using s = 6 m and √(6 × 3 × 2 × 1).
Assumptions and input details
In base-and-height mode, the second input must be a perpendicular height, not a sloping side. Three-side mode rejects flat or impossible triangles. Mixed input units are converted before calculating.
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
Choose from 23 length definitions, including explicitly labelled regional measures. Area conversions square the length factor; geometric volumes cube it.
Regional measures are not interchangeable merely because their names look similar. This is a documented selection, not a claim to include every historical unit.
NIST measurement tables · Japanese traditional units · Mainland China and Hong Kong unit distinctions
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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A little space to keep the tools free.