In SI base units, one newton equals one kilogram metre per second squared. Written symbolically, 1 N = 1 kg·m/s², so the missing unit is the second, raised to the second power.
The newton is an SI derived unit of force. Its definition follows directly from Newton’s second law: a net force of one newton gives a one-kilogram mass an acceleration of one metre per second squared. The squared second reflects acceleration, which is a change in velocity over time.
The unit was named for Isaac Newton in recognition of his work in classical mechanics. The General Conference on Weights and Measures standardized the MKS force definition in 1946, and the name “newton” was adopted in 1948. Although force has a special unit name, it can always be expanded into SI base units.
A frequent mistake is confusing metres per second with metres per second squared. Metres per second measures velocity; metres per second squared measures acceleration. Since force combines mass with acceleration, the latter is required.