The radian, denoted by the symbol rad, is the unit of angle in the International System of Units (SI) and is the standard unit of angular measure used in many areas of mathematics. The unit was formerly an SI supplementary unit (before that category was abolished in 1995).[1] The radian is defined in the SI as being a dimensionless unit, with 1 rad = 1.[2] Its symbol is accordingly often omitted, especially in mathematical writing.

An arc of a circle with the same length as the radius of that circle subtends an angle of 1 radian. The circumference subtends an angle of 2π radians.
General information
Unit systemSI
Unit ofangle
1 rad in ...... is equal to ...
   milliradians   1000 mrad
   turns   1/2π turn
   degrees   180/π° ≈ 57.296°
   gradians   200/π grad ≈ 63.662g

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