What volume boil for a 1 gallon batch?

Hey all,
I'm planning on trying out experimental 1 gal batches (from extract if it makes a difference).
Should I do a 3 litre boil and top up in the same proportions as a 5gal batch?
Presumably boiling the full gallon messes up the amount of bittering/taste you get from the hops in a recipe?
Sorry to be a newb.

It's not the volume per se that affects the hop utilization, but for a given recipe a higher volume will mean a lower boil gravity, and lower boil gravity does increase hop utilization. I personally would boil 1.25 gal so that I can save a buck or two on hops and by the time you're done boiling you should be at one gallon once the wort cools down.

Thanks! I'll browse Palmer for an equation I could use for conversions

I do full boils...around 1.7 gallons to start if that helps

If you start with 1.75 gallons you usually boil down to 1.25-1.5 gallons. After fermentation that'll leave you about 12 pack. Plus by doing it this way you can take your typical homebrew recipe and cut everything by about 25%. For example in a 6 gallon batch (6 gallons post-boil and 5 gallons finished beer) if you used 28 grams or 1 oz of hops at 60 min then you would use 7 grams. Or if you would usually have 1 pound of crystal malt you would use 0.25 of the same malt. We have some recipes and fermentors that might help your experimentation quest. Check us out here: www.smallbatchhomebrew.com