Square Foot Calculator for Triangle
Calculate the area of any triangular space using base × height, three sides, or two sides and an angle.
How to Calculate Triangle Area
There are three common ways to calculate the area of a triangle:
Method 1: Base × Height
This is the simplest method. The height must be perpendicular to the base. Example: a triangle with a 10 ft base and 8 ft height has an area of ½ × 10 × 8 = 40 sq ft.
Method 2: Heron's Formula (Three Sides)
When you know all three sides, use Heron's formula. First calculate the semi-perimeter (s), then plug into the formula.
Method 3: Two Sides + Included Angle
When you know two sides and the angle between them, use this trigonometric formula.
Triangle Square Footage Formulas
Different triangle types require different measurements. Choose the formula that matches what you can physically measure in your space:
| Triangle Type | Formula | When to Use |
|---|---|---|
| Base & Height known | ½ × Base × Height | Any triangle where you can measure straight up from the base |
| Right Triangle (two legs) | ½ × Leg A × Leg B | Corner cuts, right-angle spaces |
| Equilateral (all sides equal) | (√3 ÷ 4) × Side² | Decorative triangular tiles |
| Three sides known (Heron's) | √(s(s−a)(s−b)(s−c)) where s = (a+b+c)/2 | Irregular triangular lots |
Real-World Uses of Triangle Area Calculations
Triangular areas appear more often than you'd expect in construction, landscaping, and real estate. Here are common applications with worked examples:
Triangular Roof Section (Gable End)
A gable-end wall is a triangle. A gable 20 ft wide with an 8 ft peak height = ½ × 20 × 8 = 80 sq ft of wall area to paint or side.
Corner Lot or Pie-Shaped Land
Many corner lots are triangular. A triangular plot with a 60 ft base and 45 ft depth = ½ × 60 × 45 = 1,350 sq ft (0.031 acres).
Triangular Garden Bed
A triangular raised bed with base 8 ft and height 5 ft = ½ × 8 × 5 = 20 sq ft. At 1 plant per sq ft, that's 20 plant positions.
Attic Floor Space
Attic floors under sloped roofs form triangles. Measure the width at the base and the height to the ridge beam, then apply ½ × B × H for usable floor area.
Triangle vs Rectangle: Choosing the Right Formula
If you're unsure whether your space is a triangle or a rectangle, a simple rule of thumb applies: if the space has three corners (vertices), use the triangle formula. If it has four right-angle corners, use the rectangle formula.
- Right triangles have one 90° corner — common in cut corners of L-shaped rooms.
- Acute triangles have all angles less than 90° — typical in pie-shaped lots.
- Obtuse triangles have one angle greater than 90° — common in irregular land parcels.
For mixed shapes (e.g., a room that is mostly rectangular with a triangular bay), calculate each part separately using the appropriate formula, then add the results together. Use our Odd Shapes Calculator to handle multiple combined shapes in one calculation.
All Square Foot Calculators
Choose a specialized calculator for your specific project type.
Frequently Asked Questions
The height is the perpendicular distance from the base to the opposite vertex. For a room, you can measure from the wall (base) straight to the farthest point.
Yes! For a right triangle, the two legs are the base and height. Use Base × Height method — the area is ½ × leg1 × leg2.
Heron's formula calculates the area when you know all three side lengths: first compute s = (a+b+c)/2, then Area = √(s(s-a)(s-b)(s-c)).
Measure the longest wall (base), then measure the perpendicular distance from that wall to the opposite corner (height). Use the base × height method.