Direct answer
ScaleTrip uses 0.84075 fm for the proton root-mean-square charge radius. It describes the measured spatial distribution of electric charge, not a hard spherical edge.
Representative value0.84075 fm
In meters8.4075 × 10⁻¹⁶ m
Measurement typeCharacteristic length
Put it in context
What are we measuring at this scale?
A radius is not a diameter. Doubling the number would make a geometric diameter, but that still would not turn the proton into a rigid ball because its internal quantum structure is distributed.
Conceptual visualization
Proton charge radius
The measured root-mean-square charge radius, not a rigid spherical edge.
Source and verification
Where the value comes from
NIST 2022 CODATA recommended values
ScaleTrip keeps the 0.84075 fm range and the characteristic length label visible together.