When I am planning how to 'cut up' the interior I sometimes draw rooms to scale and plan in furniture to scale. This is really the very best idea and might stop you from chopping off the odd three inches - how can that smidgen matter? - and then discovering you now have an unworkable space. It can be very hard to do though when you have no idea of how you might furnish somewhere so, more often than not in my case, it gets chopped around and I then have to work with the space I have left myself.
I do like to mess around with stand-in furniture once I have the spaces ready to play with so I can try and get the feel of a room. This is something of a struggle this time as I only have a few sticks of furniture - I shed the rest when I went over to the dark side (switched to 48ths).
This 'playing' is pretty much essential so that you can work out where the fireplaces will come in relation to furniture and where the lights will need to go.
My dining room measures 13.5 x 15 inches which seems pretty generous until you need to get in a couple of sideboards, a chimney breast, table and six chairs with the option for eight. Trust me, it really is a quart into a pint pot. This exercise has left me with a fear of the other much smaller rooms in the house. I just have to keep reminding myself we are dealing with a modest house in Lyme Regis, not a London mansion.