I am doing chairs but was trying to figure out the rough diameter of the space

I would think 12 feet would be an average small size area for four chairs a nd fire pit .

The fire pit and surrounding stone wall looks to be anywhere from 5' to 6' diameter minimum. Then there may be about 4'-5' of stone pavement beyond that.

That would make the overall footprint here 13' - 16' in total diameter. Too large is better than too small when it comes to sitting around the campfire. One can always move back if it's too hot or smokey.

Do you have pictures of the current deck and your yard because scale is important. and you need to maintain a balance.

The deck is about 20 ft long and about 14 ft wide. I was looking to add a pea stone patio for two reasons; the first is put a fire pit there and the second is to deal with the fact that I have a dog that loves to go to the bathroom in that spot. The spot that he has destroyed right now is about 11 ft long from the step into the yard. The yard is very tiny about 50ft wide by 40 ft deep but i needed to come up with something to the bare spot and a pea stone patio/fire pit area is the perfect fit. If you have any other advise I am all ears. :)

I think a firepit in a round configuration about 12 feet should be perfect.. Spray paint a circle in the grass and see hoe that looks and if you have room and want to increase the circumference will know.. Good luck!

Where does the lid come from?

All my study leads me to believe roughly 12 X 12 is good size for 36" fire pit and four chairs. Thinking if stone random edges create opportunity to blend into landscape