I'm not going to say the number but my turnover requirement is pretty high due to making mistakes earlier in my life for which I'm still paying the debts.
However, if my only debt was my mortgage, £1,900 a month turnover would be OK. Nothing fancy but I could manage on it so long as I wasn't silly. Mind you, I don't drink or smoke and I'm OK with one modest week away each year so long as I take the odd day or weekend away for leisure pursuits.
I do actually turn over a fair bit more than that (not saying how much more as that's between me, my accountant, and the IR) but much of it is for servicing debt. It's coming down though.