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CalculateCubicFeet

Triangular Prism Cubic Feet Calculator

Find the cubic feet of any triangular prism using the triangle base, triangle height, and prism length. Perfect for wedges, ramps, attics, and A-frames.

The formula
V = ½ × b × h × L
b = triangle base, h = triangle height, L = prism length (all in ft).
Total Volume
0
cubic feet (ft³)

Enter your dimensions to see the result and instant unit conversions.

How to calculate cubic feet of a triangular prism

A triangular prism is a 3D shape with two parallel triangular faces connected by three rectangles. Its volume equals the area of one triangular face times the prism length. Triangle area is ½ × base × height, so the volume formula becomes:

Triangular prism
V = ½ × base × triangle-height × prism-length
= For b = 4 ft, h = 3 ft, L = 8 ft → 0.5 × 4 × 3 × 8 = 48 ft³
Two heights to keep straight
"Triangle height" is the perpendicular distance from the triangle base to the opposite point — measured inside the triangular face. "Prism length" is the third dimension, the depth that turns the flat triangle into a solid. Confusing the two is the most common mistake.

Worked examples

Example 1: A concrete ramp, 6 ft wide, 8 ft long, 1 ft tall at the high end

Treat the side as a right triangle: base = 8 ft (run), height = 1 ft (rise). Prism length = 6 ft (width). V = 0.5 × 8 × 1 × 6 = 24 ft³, or 0.89 cubic yards of concrete.

Example 2: A 24 × 16 × 30 ft attic with a 6 ft peak

The attic cross-section is a triangle: base = 16 ft (joist span), height = 6 ft (peak above joists). Prism length = 30 ft (front-to-back). V = 0.5 × 16 × 6 × 30 = 1,440 ft³ — useful for HVAC and insulation calculations.

Example 3: A wooden ramp wedge, 36 in long, 6 in tall, 24 in wide

Convert to feet: 3 × 0.5 × 2. V = 0.5 × 3 × 0.5 × 2 = 1.5 ft³.

Common uses

  • Concrete ramps, curb ramps, and skateboard wedges
  • Roof and attic spaces with gable ends
  • A-frame tents, sheds, and small cabins
  • Triangular planters, garden corners, and edging
  • Truck-bed wedge cargo and triangular shipping crates

Common mistakes to avoid

  1. Confusing triangle height with prism length. Both are needed and they're different dimensions.
  2. Using slant height instead of perpendicular height. The h in the formula is the perpendicular drop from the triangle apex to its base.
  3. Forgetting the ½ factor. A triangle is half a rectangle. Skipping the ½ doubles your answer.

Expert tips

  1. Identify the cross-section first. A triangular prism has a triangular face on each end and rectangular faces around the middle. Find the triangular face — that defines your “base” and “triangle height”. Everything else is the prism length.
  2. Use the perpendicular height of the triangle, not its slant height.The triangle's height is the perpendicular distance from the base to the apex, not the length of the sloped side.
  3. For attic spaces and roof volumes, the triangular prism formula is ideal. Many attics have a triangular cross-section running the length of the house. See the greenhouse / room volume calculator.
  4. For ramps, the prism length is the run of the ramp. A skateboard ramp 8 ft long, 4 ft wide at the back, and 2 ft tall has a triangular cross-section at every point along its 8 ft.

Frequently asked questions

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