Not a simple answer to your question, but...
My recipe from 2016 (about 2.5 kg sloes in total) was 500g sloes, 400g gin, 120g sugar. It was a good year, the sloes were very ripe & I probably overdid the sugar a bit though by Christmas this year the sweetness should be about right. Your taste buds will vary
. Following my family tradition, the sloes were all pricked with a fork, a process which separated them from the inevitable stalks.
I've never used a hydrometer to measure the density of sloe gin & related fruit/spirit drinks. Nor have I bothered to weigh the sloes after the liqueur has been drained (with a bit of waiting with lots of sloes in a demijohn for any late juices). Also there are losses in subsequent filtering out (a few layers of butter muslin & a BIG {unless you're very patient} funnel) of the fruity sludge.
Guesswork would be that the resulting sloe gin for my recipe is 600-700g, so might fit into a 3/4l. bottle. How heavy is a litre of gin?