@User You must use the integ function inside a

.measure

line: say you have a 0V voltage source in series with a load ad want to integrate the current:

.measure tran charge integ i(vled) from=0 to=200us

what is i want to integrate Vled current. Ngspice gives you the following report after completing the transient sim:

Measurements for Transient Analysis

charge              =   3.24060e-04 from=  1.00000e-11 to=  2.00000e-04

Okay, thanks 🙌