It’s not ignorant, Charlie, just unfamiliar. We were all unfamiliar once.
Here’s my experience, living out in the hinterlands of a jerkwater county:
TL,DR - take the larger dimension. The difference between the top and bottom will be insignificant compared to the increments any mfgr offers.
Online shopping for hatchet handles can be uncertain. If the vendor sells what you want, and has it in stock, and ships it timely, it still might be disappointing in terms of grain, shape and finish. Many BF members who buy online buy more than they need, so as to have more choices on hand.
Local shopping solves a few of those issues, but raises a few more. Expect a small selection with not all sizes represented, and no knowledgeable help. There are only a few stores “local” to me (within say, 40 miles), none of which sell many handles each year. If you need a handle on the day their annual shipment comes in, you’ve got a fighting chance to get the one you want. The day prior, the rack will be sparse and picked over. One store, I can ask the right employee when the shipment will arrive, and get a (kinda) accurate answer. No idea if other hatchet-hanging patrons are asking too. When I was buying all my handles, I made a point to stop at any hardware store I passed, and buy up any handles that met my stringent standards whether I needed them right then or not. I also bought them at swap meets and yard sales.
Making your own handles is not for everyone. It solves some of the issues above, but you guessed it, raises some others. Hickory and ash are the favored handle species- neither of them grow here. I have lots of maple, not as strong but serviceable if hung well.
Short story long, I now have a couple 5-gal buckets full of various handles. I don’t know what size will fit the head(s) I’ll buy at the swap meet next weekend, but I’m more likely to have one suitable than if I didn’t have any set back.
Best of luck in your hanging efforts, and show us how it turns out.
Parker
