There are no default units used in Abaqus, so it is users' responsibility to make sure the correct unit system is used for the analysis. Here are some commonly used systems of units:
gram-millimeter-millisecond-MPa-N
ton-mm-second-MPa-N
kilogram-meter-second-Pa-N (SI)
Additional units:
g-mm-ms-MPa-N-mJ-W-K
kg-m-s-MPa-N-J-W-K