Special Relativity Calculator

How fast the object moves, read in the unit chosen next. The effects only become large near the speed of light.

0.8 as a fraction of c gives a Lorentz factor of about 1.67.

How to read the speed above.

• fraction of c: a share of light speed, so 0.8 means 80 % of c.
• km/s: kilometres per second.
• m/s: metres per second.

A time interval measured in the moving object's own frame, in seconds.

A stationary observer sees it stretched by the Lorentz factor.

The object's length measured at rest with it, in metres.

A stationary observer sees it contracted along the direction of motion.

The object's mass at rest, in kilograms, used for the rest energy E = mc² and the total relativistic energy.