Triangular Prism Surface Area Calculator
The surface area of a triangular prism is 2 times the triangle area plus the perimeter times the length, and this triangular prism surface area calculator adds the two triangular ends to the three rectangular sides the moment you type the numbers. Enter the three triangle sides and the prism length, and you'll see the total surface area, the lateral (side) area, and the ends at once, in square inches, feet, centimeters, and meters, with the formula shown.
- All five faces
- From the three sides
- Right or equilateral
- Lateral area too
- Multiple units
Last updated June 15, 2026 Method: SA = 2A + (a+b+c)L Reviewed by the Calcowa math team
Enter the three sides of the triangular end and the length of the prism.
Enter three valid triangle sides and a length to see the surface area.
Show all units
SA = 2(6) + (3 + 4 + 5)×10 = 132 in²
What is the surface area of a triangular prism?
The surface area of a triangular prism is the total of its five faces, two triangular ends and three rectangular sides, found with SA = 2 × (triangle area) + (perimeter × length). For a 3-4-5 triangle on a prism 10 long, that's 12 + 120 = 132 square units.
The two ends are the triangle counted twice, so 2 times its area. The three sides are rectangles, and together they're the triangle's perimeter wrapped along the length. Add the two parts and you've covered the whole skin.
How do you find the surface area of a triangular prism?
To find the surface area, add the two triangular ends to the three rectangular sides. Here's the full sequence:
- 1
Find the triangle areaWork out the area of the triangular end from its three sides or its base and height.
- 2
Double it for the endsMultiply the triangle area by 2, since the prism has a triangle at each end.
- 3
Add the three sidesAdd the triangle perimeter times the length, which covers the three rectangles.
- 4
Read the totalThe sum is the total surface area in square units.
- 5
Convert the unitsConvert to square feet or square meters if that's what you need.
The two triangular ends and three rectangular sides
A triangular prism's surface splits cleanly into two kinds of face, and that's what keeps it simple. The two ends are matching triangles, so they add 2 times the triangle area. The three sides are rectangles, each one a triangle side long and the prism length wide, so together they're the lateral area: perimeter × length. The calculator lists the lateral area and the two ends on their own, which helps when you're only painting or wrapping part of the prism.
Surface area of a right triangular prism
A right triangular prism has its three rectangles square to the triangular ends, which is the everyday kind you'll meet. The formula doesn't change, SA = 2 × (triangle area) + (perimeter × length), and most prism questions assume a right prism. If the triangle itself is right-angled, its area is simply half the product of the two short sides, which keeps the numbers quick, so you'll do it in your head.
The net of a triangular prism
The net of a triangular prism is the shape you'll get by unfolding it flat: two triangles and three rectangles joined edge to edge. Adding up those five areas gives the surface area, which is exactly what the formula does. Drawing the net is the easiest way to see why it's got five faces, and why the rectangles add to the perimeter times the length.
Surface area and volume of a triangular prism
It's easy to mix these up. The surface area wraps the outside, 2 × (triangle area) + perimeter × length, and comes out in square units. The volume fills the inside, triangle area × length, in cubic units. They both start from the triangle's area, so you'll see it beside the result, and the triangular prism volume calculator handles the space inside.
A surface area example, step by step
Say you've got a chocolate bar with a 3-4-5 cm triangle end and a length of 20 cm. The right-angled triangle's area is ½ × 3 × 4 = 6 square centimeters, so the two ends are 12. The perimeter is 3 + 4 + 5 = 12, and 12 × 20 = 240 for the sides.
SA = 2(6) + 12 × 20 = 252 cm²
two ends 12 cm² + three sides 240 cm²
Type sides 3, 4, 5 and a length of 20 in centimeters above, and you'll get the matching square meters and square inches at once.
Units and accuracy
Calcowa shows the triangular prism surface area in square millimeters, centimeters, meters, inches, feet, and yards all at once. The triangle area comes from Heron's formula, so any valid triangle works, and you'll get exact conversions, which suit packaging, roofing, and school work alike.
| Unit | Best for | Good to know |
|---|---|---|
| Square inches (in²) | Wedges, hats, small panels | Default when you enter inches |
| Square feet (ft²) | Tents, ramps, roof faces | 1 ft² = 144 in² |
| Square centimeters (cm²) | Lab and school work | 1 in² = 6.4516 cm² |
| Square meters (m²) | Large structures and cladding | 1 m² = 10.7639 ft² |
| Square yards (yd²) | Roofing and big jobs | 1 yd² = 9 ft² |
Frequently asked questions
Is the area of a triangular prism the same as its surface area?
Yes. When people say the area of a triangular prism, they mean its surface area, the total of all five faces. A flat triangle has a single area, but the prism adds two triangular ends and three rectangular sides.
The surface area of a triangular prism is SA = 2 × (triangle area) + (perimeter × length). The two triangular ends give 2 times the triangle area, and the three rectangular sides give the triangle's perimeter times the prism length. For a 3-4-5 triangle on a prism 10 long, that's 12 + 120 = 132 square units.
Work out the triangle's area, double it for the two ends, then add the perimeter times the length for the three rectangles. If you have the three sides, the area comes from Heron's formula, and the perimeter is just the three sides added up.
A right triangular prism has its rectangles square to the triangular ends, so the same formula applies: 2 × (triangle area) + (perimeter × length). For a right-angled triangle, the area is simply half the product of the two short sides.
Unfold the prism into its net and you get two triangles plus three rectangles laid flat. Add those five areas and you have the surface area, which is exactly what the formula 2(triangle area) + perimeter × length adds up.
When all three triangle sides are equal to s, the area is (√3 ÷ 4)s² and the perimeter is 3s, so SA = (√3 ÷ 2)s² + 3sL. Enter the same value for all three sides and the calculator handles it.
Yes. The area of a triangular prism means its surface area, the total of all five faces. A flat triangle has one area, but a prism adds two triangular ends and three rectangular sides.
Multiply the triangle's area by the prism length: V = (½ × base × height) × length. This calculator shows the triangle area next to the surface area, and our triangular prism volume tool covers the space inside.
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