I wouldn't worry about exactitudes. I've never done a half pie, per se, but I've read that 7" is half. I have made four inch-ish pies, both from mini-pie molds and in little ceramic pie dishes. IIRC, one batch of dough and filling makes three in the pie dishes. The baking time is easier--I'd do about 2/3 of the time called for to start with and check for bubbling and browning and add time from there if needed.

You could just experiment. Make one half recipe, roll out your dough and see which dish it best fits--I'd guess the biggest one, and see how much you have leftover, if you have any, and make notes for next time. If you have a lot of left over, you can make a mini pie/tart in the smallest dish even if the dough isn't big enough to completely line the dish.

graywings, make the entire pie. I will be over to eat the other half.

They sell half-pie or divided pans. What you might do is to use a porcelain plant pot saucer. I’ve got a couple (porcelain, high fired, not low fired). Sleevendog commented a few days ago on using one for something. Mine are about 6.5” or 7” in diameter. You could also use a Pyrex casserole bowl flat cover. Or, you could fold the crust sides up as one would for a galette.

Foto from web

Interesting question. If you went strictly by the area of the pie plate, then a 6.5" plate would be close to half of the area of a 9" plate. In your case, I'd use the deep 5.75" plate for half the recipe.

Get a measuring cup and fill the various pie plates with water, then measure how much they hold. That will tell you is you are dealing with half or 2/3 or whatever.

Make the full recipe for the crust....and if there is any left over. roll it out and using a small cookie cutter make crisps to be used on top of salads

Woo-hoo! Turns out I have a 6 inch glass pie pan. I don't remember ever using it.

Any ideas on the cook time if a full pie needs an hour to bake? The recipe calls for cooking it in a brown paper bag, so gauging it by appearance would be tricky.

"I wouldn't worry about exactitudes. I've never done a half pie, per se, but I've read that 7" is half."

That's actually worked well for me with a small, 7" ceramic pie pan I have (measuring from the inside edges). It's also just short of 2" deep. It was for a pecan pie, and the baking time was just a little less...as I recall.

Depending on the recipe, petalique's suggestion of a galette/crostata would also work.

Because the thickness will be about the same and the volume isn't that much smaller, I don't think the time would be changed by much - maybe check it 10 minutes or so early. You can open the bag and then put it back in if it needs to cook more.

What kind of pie bakes in a brown paper bag? I'd be more concerned about cooking time if it is something more delicate like a custard.

P.S. you got the answer for this time, but for the future, the depth isn't changing so basically, you want a pie plate with half the area of a 9" pie plate. (That's approximate because the sloped sides may affect the volume a bit as diameter changes, but it should be close enough.) Area is proportional to the square of the diameter. So, when you want to divide area by 2, you divide the diameter by the square root of 2. 1.4 is close enough. 9 divide by 1.4 is about 6.4 or close to 6 1/2.

I've not made a traditional two crust pie ever that I can remember. I do have a couple pie tins and a glass one from a yard sale. For fruits I like a rustic galette.

I fell for the tart tins with the removable bottoms years ago and have many. Different heights from one inch to three. Most are the small 7inch diameter.

Cooking time reduction varies depending on the height and the filling. Berries are forgiving but some fillings are problematic. (I add fresh berries halfway through cooking on top.) If the recipe cooking time is one hour, I count on 20 minutes less. If the cooking time is 45 minutes, I count on 15 min less. Really depends on the height/density.

Pecan pie, a family favorite, gets so dry/gritty if overcooked. (did that once)

I do the same with crust. Never cut the recipe. The overhang gets turned into decoration for the edges. Usually a tiny oak leaf cutter. DH is the pie crust maker so always have some in the freezer. Frozen as singles. One party I took out two thinking I might make two different pies/tarts. Just made one knowing the crowd would just want a sliver. (Dad will take a sliver, then 4 more slivers 🙄)

The second crust I rolled out and started adding grated cheese half way through the rolling and made cheesy crisps. Nice pre-dinner snack. So you can always freeze or use that extra crust for other things like pot-pies or hand pies.

Not made a pie at all this covid mess. Just eating our fruit fresh. Shame. Not even a custard.

I always freeze the other half pie or cake. If I bother making a pie or cake, I am not cutting it in half. they freeze perfectly.

I agree that 6" to 6.5" would be an acceptable diameter. 6.36" diameter would be exactly half of a 9" diameter. However, you have to take into account the slanted sides, and so I think 7" diameter would be ideal, but 6" diameter is probably close enough. I do my calculations by taking the square of 9 (which is 81), divide that by 2 (which is 40.5) and take the square root of that, which is 6.36".

make a regular size pie and freeze the remaining pieces for later ...

When I was a child, my mother asked me to cook a roast chicken dinner. I must have been about 9. I asked her how I would know when the chicken was cooked. Look at it, she said. You've seen enough cooked chickens. She wasn't wrong lol . I think the same thing would go for your pie. But, as has been said, I'd cook the whole thing and share/freeze it.