For a reference, the Space Shuttle Orbiter, an atmospheric entry capable real-life spacecraft that weighs ~68 tons empty or ~110 tons loaded would need a hangar so big that it would store more than 3500 tons of cargo* if used as a warehouse. That's a ratio of 1:35.
This is assuming that your hangar is a plain box. If you customize your hangar to fit your atmospheric craft's geometry, I believe you could get significant savings, but it's still something like 1:20.
If you also optimize your craft and add features like folding wings and control surfaces (like on naval fighter jets on aircraft carriers) I believe it is possible to store and field 1 ton of spacecraft in the space needed for 10 tons of cargo. ie. 1:10
A real life cylindirical spacecraft like the Apollo command+service module is much more effective in that sense. It weighs ~12 tons and approximately fits in a cargo hold that could fit 36 tons if needed, for a ratio of 1:3. Keep in mind that it is a very frugal spacecraft with just 6 cubic meters of interior space for three astronauts.
By the way, 1:3 is also the ratio for a typical car.
The International Space Station is more like a distributed spacecraft, made up of connected modules, and in its assembled and deployed state, the same calculation gives a number more like 1:78
If I would make a ruling on this, based on hull configurations in the Traveller SRD, I'd go for 1:4 for standard, 1:16 for streamlined and 1:80 for distributed. If the daughter ship has provision for stowing or folding ptrousions like wings, radiators and solar arrays, I'd make the numbers 1:3, 1:8 and 1:20 respectively.
Zeiss Ikon mentioned the Traveller Classic rule about cargo space, standardised for liquid Hydrogen. If that is the weight/space ratio they had in mind (~75kg/m³), then my assumptions become something like this (rounded for simplicity):
2:3 for standard (1:1 stowed)
1:6 for streamlined (1:3 folded)
1:30 for distributed (2:15 stowed+folded)
* Assuming a 200kg/m³ average density as most cargo companies do today