This does depend on your budget and where the artwork will go in your home.
The standard is my most popular size, either A4 (to fit a standard A4 frame) or a 20cm x 20cm square (to fit a 10 x 10 inch frame) at £225
This size works well not just for a wall but also for a shelf or a desk, it's a bit more mobile.
My large size is A3 and will fit a standard A3 frame, this can also accommodate more than one dog at £350 for a large single dog or a double portrait with up to 2 dogs
For anything larger (I can work up to A2 in size) please get in touch to discuss your requirements and I can quote on an individual basis - firstname.lastname@example.org