Convert Percent Speed of Light

A simple calculator for converting percentages of the speed of light to other units of speed.. The speed of light is extremely high, nearly 300,000 kilometers per second in a vacuum. Other speeds are often misjudged in comparison, as the speeds we typically encounter are in the range of small fractions of one percent of the speed of light. To illustrate high speeds, it can be helpful to express them in several units, in familiar ones like kilometers per hour and in less common ones like kilometers per second. Objects with mass, whose speed is usually expressed relative to the speed of light, mostly come from the realm of particle physics. Electrons can easily reach speeds exceeding 90 percent of the speed of light. For macroscopic objects, a speed in the percentage range of the speed of light in space would theoretically be possible, although difficult to achieve, as it would require enormous amounts of energy. In the atmosphere, however, air resistance practically prevents such speeds.
The speed of light in a vacuum is preset, this can be changed for a different medium. Please enter one of the following values ​​to calculate the other speeds.

The reason why objects with mass cannot reach the speed of light, and why approaching it is very energy-intensive, is relativistic mass increase. This is an aspect of special relativity. Other interesting aspects related to this are time dilation and relativistic velocities.

Physics commonly uses SI units. Here is a calculator to convert units.