I have a 45 inch. Seats 4 very well....and will seat 6 but not much room for anything but your plate, silverware and a glass. But, because of the curve of a round table you never bump elbows. When I had just small straight chairs I regularly sat 5 and6 ...but now I have larger chairs and one arm chair...5 is about all any more.
If you are a family of 5 and will use it daily and have the room, I would go for a 50 or a 54 inch table.
My table has survived toddlers....and even those toddlers toddlers....please don't put glass on your table.
Linda C

Agree to avoid the glass.

They make table covers that look like the table-top and are custom-fit inside with felt lining to keep the surface like new. Also heat-resistant up to 500 degrees. Ask about one of these products when you are shopping for your table.

A 54" table is usually sold with 6 chairs. Another consideration would be a 48" table that leafs out into an oval. It's standard for 48" tables to come with only 4 chairs but the store should be able to order another pair for you. If I were doing this, I would have them agree in writing that the 2 new chairs have to match the other 4. Sometimes there can be color variations in different "batches." Another difficulty with trying to permanently use a 48" table with 5 chairs is that the 5th chair needs a home. It won't fit under the table.