Time Dilation & Length Contraction

Calculate special-relativity time dilation, the Lorentz factor and length contraction at a fraction of the speed of light, free online.

Speed (% of the speed of light)

Time on the moving clock (any unit)

Rest length (any unit)

About this calculator

The Lorentz factor is γ = 1 ÷ √(1 − v²/c²). A moving clock runs slow: Δt = γ·Δt₀, and lengths along the motion contract: L = L₀ ÷ γ. At 90% of light speed γ ≈ 2.29.