Triangle Calculator Guide: Formula & Worked Example
Short answer
Area, perimeter and angles from three sides. In the fixed example below, area is 14.696938. Your answer depends on the inputs and assumptions you choose.
Formula
Heron: A = √(s(s−a)(s−b)(s−c))
Use the relationship above with consistent units. The inputs are side a, side b, side c. Use the input scale shown beside each field and keep time periods and units consistent. Only round the final result for display.
Worked example
- Side a
- 5
- Side b
- 6
- Side c
- 7
- Area: 14.696938
- Perimeter: 18
- Angles A / B / C: 44.415° / 57.122° / 78.463°
Understanding the result
Area, perimeter and angles from three sides. Start with the base example, then replace each value with the figure that matches your situation.
Side a
The example uses 5 for side a. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
Side b
The example uses 6 for side b. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
Side c
The example uses 7 for side c. This is an illustration, not a recommended value. Keep the unit and time period shown by the field.
What the comparison means
The comparison changes only side a, keeping every other example input fixed. This isolates that input's effect on the primary result. It does not predict future outcomes.
Check units, date boundaries and rounding before using the answer in a report or a practical measurement.
Comparison
| Scenario | Input | Result |
|---|---|---|
| Lower input | Side a: 4 | Area: 11.97654 |
| Base example | Side a: 5 | Area: 14.696938 |
| Higher input | Side a: 6 | Area: 17.05689 |
Common mistakes
- Using the wrong units for side a.
- Comparing results while changing more than one input at a time.
- Check units, date boundaries and rounding before using the answer in a report or a practical measurement.
Checklist
- Confirm side a.
- Confirm side b.
- Confirm side c.
- Check the result against your source or provider.
Calculators Percentage Editorial Team
Calculator guides from the Calculators Percentage team. These introductory examples are educational, not professional advice.
Last reviewed:
Check units, date boundaries and rounding before using the answer in a report or a practical measurement.