How about filling it to your desired level and emptying into a vessel of known volume eg empty milk bottle etc. Or, weigh the water it contains because 1 kilo weight equals 1 litre water.
sorry maggiebee - I'm sorry I am so like yourself as I am despondent too and so RH could not be bothered wandering around shops for a measly jug - just want to order online and get rid.
Assuming it's a roughly cylindrical jug, I would estimate it's something between 6.5 and 9.5 litres, depending on whether you measured the inside or the outside. That does feel to me to be too large. But if you have a measuring jug anywhere, you can also find out by filling it up and seeing how many times you can fill your measuring jug from it.
maggie - do think I ask questions probably way out of your league as they have been technical lately especially regarding that Full Fibre thing that I hope you will never come through.
Nothing is going right and yes it is so fabulous to be able to hear and Telephone yourself NOT. Be very very grateful you have your hearing and listen out for Option 1 press this option 3 press this - then me, I give up and hang up.
so sorry if asking about a simple jug bothers - sorry again.