Just whipped my tape out and measured the boot but bear in mind this is for a 159 Sportwagon!
Approx' Measurements (all in cm) as follows:
Height of boot space from floor to roof - 72
Width of floor at rear of boot (due to slight inset of wheel arch) - 94
Width of floor nearest boot lip - 106
Depth from rear seats to boot lip (at all points) - 95
[Note that there is a ski hatch as well as 60/40 folding rear seats that greatly extend this if needed]
Boot lip height - 25
Boot entrance width (at widest 'top' point due to tapering) - 100
Boot entrance width (at narrowest 'bottom' point) - 84
I have to say I'm pleased with the boot space and I haven't had any issues even with a 10 and 2 year-old plus baggage etc. and putting prams/buggies in. Only an adult sized bike has been a pain (unless you took front wheel off) due to the tapered entrance. I had to put the seats down and therefore couldn't take any rear passengers.
Also, it's good to have 4 cubby-holes that can fit the manual/torches/tyre inflator etc and there's also rear lights, luggage nets at base, rear and sides as well as a rear cigarette lighter which is handy for charging things.
Hope this helps?