what size tire is best for a 92 honda civic four door gas saving wise?

the size that fits the wheels. It’s your foot that saves petrol nothing to do with the tyres.

The stock size. possibly a bit narrower, but you have to think, if honda could have done anything to improve gas mileage, they probably would have done it.

It will be the stock tire size which should be 195/60R14. Although to be certain, look at the sticker located on the driver side door jam. Switching tire sizes will not get you any fuel savings. Now going to a lighter wheel will help fuel cost a fair bit.

Open your gas tank cover. There should be all information and recommendation about tires and weel for your vehicle.

The size isn’t as important actually. Get the proper size for the car, but look for something that is “low rolling resistance”.

The size it was equipped with at the factory, as listed on the Tire Load and Inflation tag inside the drivers door.