By Zencalcy Editorial TeamLast reviewed About us
The coefficient of restitution measures how much of the relative speed a collision returns. Dropping a ball is the easiest way to measure it: the ratio of rebound height to drop height is the square of the coefficient, so the coefficient is the square root of that ratio.
Bounciness from drop and rebound height.
e = √(h₂ / h₁) h₂ = e² h₁
h₁ is the drop height and h₂ the rebound height, both measured from the same reference. e = 1 is perfectly elastic, e = 0 is perfectly inelastic; a typical basketball is around 0.75–0.8.
| Symbol | Meaning |
|---|---|
| e | Coefficient of restitution, dimensionless, between 0 and 1. |
| h₁ | Drop height, in metres. |
| h₂ | Rebound height, in metres. |
The ratio is 0.64, so e = √0.64 = 0.80. The square, 0.64, is the fraction of kinetic energy retained; 36% is lost to deformation, sound and heat.
Continue with the Drag Force Calculator, Force Calculator, or the Gravitational Force Calculator — or browse more dynamics tools and all physics calculators.
Ideal models treat it as a material property, but real balls lose a slightly higher fraction at higher impact speeds. For school-level work a single value is usually adequate.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Content updated: September 2026