Trying to match a duvet that says 400g per m2

[worriedsick100]

I am trying to match a french duvet which has no to value on it but says 400 g per m2. Anyone got any idea what tog value this is? Thanks.

From what I've found, it depends on what it's filled with - as the density can be different dependent on the filling apparently - sorry to be of not much help :(