The mass of one neutron is approximately 1.0086649156 atomic mass units (amu).

To convert this to kilograms, you can use the following conversion:

1 amu = 1.66053906660 × 10^-27 kg

Therefore, the mass of one neutron in kilograms is:

1.0086649156 amu * (1.66053906660 × 10^-27 kg/amu) = 1.674927471 × 10^-27 kg