Calculate the missing side or hypotenuse of a right triangle from any two values, with results in inches, feet, yards, centimeters, or meters.
Reverse Hypotenuse Formula
Use this calculator when you know the hypotenuse and one side of a right triangle and need the other side. Keep both inputs in the same unit so the result is returned in that same unit.
Variable Guide
| Term |
Meaning |
| Hypotenuse |
The longest side of the right triangle. |
| Known side |
The leg length you already have. |
| Unknown side |
The missing leg calculated from the other two values. |
| Units |
Use one unit system throughout: inches, feet, yards, centimeters, or meters. |
How to Calculate the Missing Side
- Square the hypotenuse.
- Square the known side.
- Subtract the known-side square from the hypotenuse square.
- Take the square root of the result.
Examples
S_2 = \sqrt{50^2 - 20^2} = 45.826
S_2 = \sqrt{30^2 - 10^2} = 28.284
| Hypotenuse |
Known Side |
Unknown Side |
| 50 |
20 |
45.826 |
| 30 |
10 |
28.284 |
| 13 |
5 |
12 |
Input Rules
- The hypotenuse must be longer than the known side.
- This calculation applies only to right triangles.
- If both values are equal, the result is zero, which is a degenerate case rather than a true triangle.
- If the value inside the square root would be negative, the inputs are not valid for a right triangle.
Quick Reference
| Situation |
What to Check |
| Mixed units |
Convert all measurements to one unit before calculating. |
| Unexpected answer |
Make sure the larger value was entered as the hypotenuse. |
| Need more precision |
Round only the final result, not the intermediate squares. |
| Sanity check |
The missing side will always be shorter than the hypotenuse. |
Common Uses
| Application |
Known Measurements |
Find |
| Roof framing |
Rafter length and one leg |
Remaining rise or run |
| Ladders |
Ladder length and wall height |
Distance from the wall |
| Ramps |
Ramp length and rise |
Horizontal run |
| Layout and surveying |
Diagonal distance and one side |
Perpendicular offset |