A current-bearing wire experiences a force when acted on by a magnetic field from any source (it doesn't have to be another current).
The magnitude of this motor effect force was proportional to three quantities: field strength (B), current in the wire (I), and length of the wire acted on by B (l).
If the wire lies at right angles to B, and assuming the field is uniform over the length of the wire, then the formula is simple:
F = BIl
If the wire (and hence current, I) makes an angle 0 (theta) with B, then a sin0 (theta) term must be included:
F = BIlsin0.
Or you can just use Danger's/Excel's definition.