Angles that sum to a straight line (180°) or right angle (90°).
Complementary Angle45.0°
θ
180°-θ
About this calculator
What are Supplementary Angles?
Two angles are supplementary if the sum of their measures is exactly 180 degrees. When joined together at a vertex and sharing a side, they form a straight line. The word 'supplement' comes from Latin 'supplere', meaning to complete.
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Pro Tips
Supplementary angles sum to a straight angle (180°).
Complementary angles sum to a right angle (90°).
Supplementary angles do not need to be adjacent (touching) to be considered supplementary.
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Fun Facts
"If one angle is acute (< 90°), its supplement must be obtuse (> 90°)."
"Vertical angles are equal, but adjacent angles on a line are always supplementary."
"In navigation and carpentry, supplementary angles are used to ensure parts fit together in a straight line."
