Direct answer
One femtometer (1 fm) equals 10⁻¹⁵ meters: one quadrillionth of a meter and one thousandth of a picometer. It is a unit marker, not a standalone particle.
Representative value1 fm
In meters1 × 10⁻¹⁵ m
Measurement typeCharacteristic length
Put it in context
What are we measuring at this scale?
The proton charge radius is about 0.84075 fm, while heavy nuclei span several femtometers. Those values may describe radius, diameter or charge distribution, so their measurement labels matter.
Conceptual visualization
One femtometre
A quadrillionth of a metre, the natural unit of nuclear dimensions.
Source and verification
Where the value comes from
ScaleTrip keeps the 1 fm range and the characteristic length label visible together.