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In trigonometry, the gradianalso known as the gon (), grad, or gradeis a unit of measurement of an angle, defined as one-hundredth of the right angle; in other words, 100 gradians is equal to 90 degrees. It is equivalent to of a turn, of a degree, or of a radian. Measuring angles in gradians (gons) is said to employ the centesimal system of angular measurement, initiated as part of metrication and decimalisation efforts. (1995). 041298511X, Chapman & Hall. 041298511X
In continental Europe, the French word centigrade, also known as centesimal minute of arc, was in use for one hundredth of a grade; similarly, the centesimal second of arc was defined as one hundredth of a centesimal arc-minute, analogous to decimal time and the sexagesimal minutes and seconds of arc. The chance of confusion was one reason for the adoption of the term Celsius to replace centigrade as the name of the temperature scale.. On p. 42 Frasier argues for using grads instead of radians as a standard unit of angle, but for renaming grads to "radials" instead of renaming the temperature scale.
Gradians (gons) are principally used in surveying (especially in Europe),
and to a lesser extent in mining and geology. (2025). 9781482262889, CRC Press. ISBN 9781482262889 (2025). 9783540746713, Springer Science & Business Media. ISBN 9783540746713
The gon (gradian) is a legally recognised unit of measurement in the European Union and in Switzerland. However, this unit is not part of the International System of Units (SI).
Although attempts at a general introduction were made, the unit was only adopted in some countries, and for specialised areas such as surveying, mining and geology. Today, the degree, of a turn, or the mathematically more convenient radian, of a turn (used in the SI system of units) is generally used instead.
In the 1990s, most scientific calculators offered the gon (gradian), as well as radians and degrees, for their trigonometric functions. In the 2010s, some scientific calculators lack support for gradians.
| 0 gradians |
| 100 gradians |
| 200 gradians |
| 300 gradians |
| 400 gradians |
One advantage of this unit is that right angles to a given angle are easily determined. If one is sighting down a compass course of 117 gon, the direction to one's left is 17 gon, to one's right 217 gon, and behind one 317 gon. A disadvantage is that the common angles of 30° and 60° in geometry must be expressed in fractions (as gon and gon respectively).
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