a = 38°
b = 90° − 38° = 52°
Angle relationships without guesswork
Complementary Angles Calculator
Find the missing angle, verify a pair, and switch between degrees and radians while the right-angle diagram updates.
Free to use. No account required. Your inputs stay in this browser.
The essential relationship
a + b = 90° = π/2
Two angles are complementary when their measures add to one right angle: 90 degrees or π/2 radians. They do not need to be adjacent. The calculator keeps full precision internally and rounds only the displayed result.
Worked examples
Follow the numbers, one step at a time
a = 22.5°
b = 67.5°
one acute angle = 61°
other acute angle = 29°
Built for understanding
More than an answer box
Every result includes the rearranged formula, substituted values, and a reasonableness check. Use the visual to connect the symbols to the measurement.
- Instant, private, browser-based calculation
- Decimal-friendly input and validation
- Responsive layout for phones and classrooms
- Copy-ready answer with units
Method and references
Formula basis
The formula follows standard textbook definitions. Unit symbols follow SI guidance; results are educational estimates, not engineering certification.
- OpenStax, Angles
- NCTM geometry conventions
Quick answers
Frequently asked questions
What are complementary angles?
Two angles whose measures add to 90 degrees.
Do they have to touch?
No. Adjacency is not required; only the sum matters.
Can complementary angles be obtuse?
No. Both must be acute, except the limiting case involving 0°.
Complementary vs supplementary?
Complementary angles total 90°; supplementary angles total 180°.
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