Right Triangle Perimeter Calculator
Calculate a right triangle’s perimeter from its two positive perpendicular legs. The tool finds the hypotenuse and adds all three sides.
How to use Right Triangle Perimeter Calculator
1. Choose Measurement Unit, then enter Leg A, Leg B without a unit suffix. 2. Use the selected ordinary, square or cubic unit for each measurement as explained below; changing the selector relabels inputs and does not convert them. 3. Select Calculate, or press Enter, and read right triangle perimeter. 4. Select Select Copy result to copy the answer, or Reset to clear the form.
Why use this tool?
Estimate the complete boundary length of a right-angled triangular feature when the sloping side has not been measured.
How the calculation works
Hypotenuse = √(leg A² + leg B²); perimeter = leg A + leg B + hypotenuse. Results use up to six decimal places. Tiny nonzero results below 0.000001 use scientific notation with six significant digits. Browser floating-point arithmetic can introduce small rounding differences. Inputs and calculated magnitudes must not exceed 9,007,199,254,740,991. Negative physical measurements and arithmetic underflow are rejected. Zero dimensions are treated as a degenerate limit where the formula allows them; divisors and sides of an actual triangle must be positive. Formula reference: https://openstax.org/books/prealgebra-2e/pages/c-geometric-formulas
Example
Leg A = 6 cm and Leg B = 8 cm give a 10 cm hypotenuse and a perimeter of 6 + 8 + 10 = 24 cm.
Practical tip
Enter the two sides that meet at the right angle. Each must be greater than zero.
Frequently asked questions
Do I need to calculate the hypotenuse first?
No. The tool calculates it from the two legs using Pythagoras, then includes it in the perimeter.
Does this work for any triangle?
It assumes a right angle between the two entered legs. For another triangle, enter all three measured sides in the Triangle Perimeter Calculator.
Does changing Measurement Unit convert my numbers?
No. The selector states the unit of the numbers you enter and labels the answer. Convert measurements first when changing units. Area inputs use square units and volume inputs use cubic units; result precision follows the rounding method above.