# 1.3 Units

Abaqus™ has no units and it does not perform unit conversions. You are responsible from using a consistent system of units. For structural analysis, a system is defined by [mass, distance, time]. The force is a derived quantity. If you choose the system to be [Kg, m, s], then force is in Newton, i.e., N=Kg m/s . Stress and modulus of elasticity is then Pa=N/m , and so on.

You can use an alternate system such as [Force, distance, time], i.e., [N, m, s], which is often more convenient. The mass is then derived : Kg=N s /m.

You don’t have to use one of the base systems, like [N, m, s]. In fact, if the most common dimensions used in your parts is mm, you should use [N, mm, s]. Then stress and modulus of elasticity will be in MPa=N/mm . The best is to use a system that allows you to express everything with numbers close to 1. In that way, you reduce rounding errors. That is not always possible, but and effort should be made. The machine precision is limited and so is your ability to work with data and results like 0.000000123 and 1.23E+07. Right?