The age-old bread tin problem

Hi

I've been baking bread successfully for a while now (not sourdough - I've tried & failed so many times that I've given up).

My problem is to do with bread tins. The one I use at present is fine. If I fill it to the very top with water it comes out at 2.5 litres. The recipe I use with this is 500gm of flour & 320ml of water etc. It works.

Now I'm after two tins, each half the size of my current  one.

But tin sizes are extremely confusing. Some tins are measured by weight (of dough I assume) such as 1lb, 2lb etc or capacity in pounds.
Other tins are measured by dimensions -  height, width & depth.

But of course all bread tins have a larger top area than bottom area so to me dimensions are of little value. The only sure fire method I can see is to measure them by volume of water but I've yet to find a supplier that measures them this way.

I now have several tins that, according the suppliers specification should be the correct size but when you check the volume they're different!

So, what I'm after is a couple of tins, each half the size of my current tin so that I can bake two smaller loaves, using the above recipe quantities

Any suggestions?