Assuming the following formula (from the wiki):
- fuel = weight/200 * distance * efficiency * (0.85 if IFE else 1)

It turns out I needed to make the following extra assumptions to make it work:
- distance is rounded UP (e.g. 79.1 -> 80)
- fractional distances larger than warp^2 are rounded DOWN (e.g. 81.54 -> 81)
- consumption per turn is rounded UP