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A unit of force specifies the reference magnitude used to express a force. The SI derived unit is the newton, defined by $1\mathrm{N}=1\mathrm{kg}\mathrm{m}{\mathrm{s}}^{-2}$, consistent with Newton's second law.

A force of one newton gives a one-kilogram body an acceleration of one metre per second squared when it is the net applied force. A kilogram is a unit of mass, so it cannot replace the newton without also specifying an acceleration or a conventional gravitational reference.^[ref]

A unit of mass is a reference for expressing mass. The SI base unit is the kilogram; the gram is $10^{-3}\mathrm{kg}$. A unit of mass differs from a unit of force: a balance may infer mass from a gravitational force, but a newton measures force and is not another name for a kilogram.

In a weighing experiment the relation $F=mg$ connects the two, with local gravitational acceleration $g$. An instrument calibrated to display mass therefore incorporates a reference or an assumed local $g$. Moving a force-sensing instrument to a different gravitational environment can change that inference even though the specimen's mass is unchanged.^[ref]