Gradian (grad)

General & non-SICurrent unit

One 400th of a full turn, so a right angle is exactly 100 gradians. Used in surveying in parts of Europe, also called the gon.

1 gradian = 0.0025 turns (exactly).

About the gradian

The gradian came out of the French Revolution as part of the push to make measurement rational. It was first called the grade, and it divides the right angle into 100 parts, so a full turn is 400 grads and one grad is 0.9 degree. In northern Europe the word grad already meant an ordinary degree, which caused confusion, so the name gon was adopted, first regionally and later internationally. Gon is the symbol given in ISO 31-1, Annex B.

The link to the meter explains the appeal. The meter was originally set at one ten-millionth of a quarter of Earth's meridian, so one gon of arc along the surface spans about 100 kilometers and one centigon about 1 kilometer. Surveyors, mainly in Europe, still use it, along with some mining and geology work, and it is legally recognized in the European Union and Switzerland. It is not part of the SI, and the SI Brochure does not mention it. Many scientific calculators of the 1970s through the 1990s offered a gon mode, though some recent models have dropped it.

Sources: Wikipedia: Gradian; NIST Guide to the SI, Appendix B.8 (angle conversion factors); MDN Web Docs: CSS <angle>

Gradian conversion chart

1 gradian expressed in every other angle unit:

More General & non-SI units

• degree (angle)
• turn (angle)
• arcminute (angle)
• arcsecond (angle)
• right angle (angle)
• octant (angle)
• sextant (angle)
• piece (counting & quantity)
• pair (counting & quantity)
• score (counting & quantity)
• hundred (counting & quantity)
• thousand (counting & quantity)
• million (counting & quantity)
• billion (short scale) (counting & quantity)
• trillion (short scale) (counting & quantity)
• billion (long scale) (counting & quantity)

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