MEASUREMENTS AND PURCHASE DECISIONS
Choose a triangle measurement method.
Which triangle inputs can be measured reliably for your boundary?
Use the matching calculator
Use this decision sequence
- Use base and perpendicular height if that height can be measured.
- Use three edges when an altitude is inaccessible.
- Use two edges and their included angle only when that angle is known.
- Check that entered edges form a non-degenerate triangle before using area.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Base and height | The height must be perpendicular, not a sloping side. |
| Three sides | Heron’s formula needs a valid triangle. |
| Two sides and angle | The angle lies between the two entered sides. |
Worked comparison
A 3–4–5 triangle has area 6 m². The base-and-height method gives 4 × 3/2 = 6; Heron’s method uses s = 6 and sqrt(6 × 3 × 2 × 1) = 6. Entering 5 as the height would overstate area.
Check before using the estimate
Do not substitute a convenient edge length for an unmeasured perpendicular height.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.