T4 Contragrav is close to T5 Lifters, and well defined in FFS:
10 kN ≈ 1 tonne of thrust.
Thrust factor is the fraction of thrust available for propulsion.
T4 FF&S, p65:
Also note that in level flight, the lift must equal the weight, and hence the maximum thrust available, in kN, will be equal to 10 x Thrust Factor x Loaded Mass.
In effect it can be used for very slow propulsion, generally combined with some other form of propulsion.
Example:
A 100 Dt ship would be roughly 1000 tonnes, requiring 10000 kN contragrav.
A TL-12 10000 kN contragrav drive would have a volume of 10000 × 0.002 = 20 m3 ≈ 1.5 Dt.
It would require 10000 × 0.0007 = 7 MW power [does not scale well to CT] and cost 10000 × 0.000020 = MCr 0.2.
A M-drive 1 in T4 would require 25 MW, so the contragrav requires about a quarter of that, perhaps a quarter of an EP [62.5 MW] translated to CT.