Energy weapons are .8 of the mech-scale weight, missiles and ballistics like MGs or APGR are less.

ERML: 1 ton -> 800 kg (0.

ML: 1 ton -> 500 kg (0.5)
SL: 0.5 ton -> 200 kg (0.4)
However:
ERML + 5xSHS: 6 tons -> 800 kg (0.133)
ML + 3xSHS: 4 ton -> 500 kg (0.125)
SL + 1xSHS: 1.5 ton -> 200 kg (0.133)
MG + 50 rounds: 0.75 tons -> 100 kg (0.133)
Huh... I remembered it being slightly higher. Anyway, I'd say it's pretty clear.