What's the Perfect Soap Size?

I prefer 3 - 4 ounces of soap in a 3.5 - 4 inch diameter container with at least 0.5 inches of load space.

I did not measure it but I find the width and the room to load in the SoapCommander and Razorock pucks to be very good. (the new stackable Razorocks)
Also their width is OK.

I really do not care how much soap is in there as long as the price/oz is fair for the product included.
Of course if you put as much in as SoapCommander you prolly get 150 shaves out of the jar, so a re-buy will happen later.

So I think marketing wise the soap maker has to evaluate if he wants a re-buy to happen because the user runs out of soap earlier or he is confident he uses more soap... or he has many great scents and the client will wan to buy them all anyways, no matter how much he used from previous purchases.
Classical marketing decisions.

Classic thing that happened to toothpaste makers. The market was saturated and people at least brush their teeth 2 times a day. So toothpaste use was no more increasing. What they did, they all (like a cartel) decided to get in bed with the brushmakers. They all decided to widen the outlet of your toothpaste tube just a tiny bit every 2 years, so you wont recognise and make the brushes a little longer (you know you want to put paste all over that brush dontcha).... magically we all use more toothpaste every 2 years. Market is growing, all are happy... you say I am nuts? Just check out a pic of a toothpaste tube from the 70s and now and you think the hole in there is HUGE now.

Wow,  this topic generated a lot more discussion than I had anticipated. 

Great feedback, keep it coming!

I have flip flopped my opinion on this a bunch of times over the years, but now I think i have a real preference. I like my tub to be around 3.5 inches in diameter and not filled to the top. Also I'm not a fan of tall tubs, it took me forever to order anything from Soap Commander because I don't like the space it takes up (holy cow that's good soap though!) I actually prefer soaps with only 3-4 oz inside simply because every time I get a 6oz soap I feel a little guilty knowing there's a better than 90% chance it will never get completely used!

The bigger the better.Check what people say about lpl for instance...it is too small!

I prefer 3 - 4 ounces of soap in a 3.5 - 4 inch diameter container with at least 0.5 inches of load space.

This works for me too.

PAA's large, 5" tinr is really too large.  Although I can hold it in my hand, it's a bit of a stretch. Along the same line, the 3" tin that WSP uses with their rustic line is really on the small size.  The Goldilocks size is  the 4"  tin that Dr. Jon and Mike's Natural use.  Despite being easy to stack and having an "old time" vibe, the downside of tins is they are easily dented by the retailer, delivery or home user.

This exactly.  I think somewhere around 5 ounces in something with a 4" diameter is just right.  It does seem a little easier to reuse the tubs than the tins.

Since I evaluate a soap's value partially by cost/oz, I would lean towards leaving a little bit of room in the container for the first handful of loads to prevent any waste, but it's not really a deal breaker or anything.

My favorite container size and soap:container ratio thus far has to be razorock (I haven't measured the dimensions). The diameter of the jar is ample size to get almost any size knot in there for loading, and the soap recess in the jar is sufficient to prevent any overflow when loading.

I love soap commander containers! 6 ounces of soap with plenty of room to load. However, they are a bit big and high profile so not easy to store or stack but excellent size! Catie's Bubbles 8oz soaps containers make them seem smaller then it really is. The small PAA tins are a good size but have not room to load. Razorock tubs are some of the best size and loading room equivalents.

I personally prefer wider tubs with a bit of head room, B&M and CRSW are my favorites. Caties Bubbles fills right to the top, but because it's a soft soap and loads easier, it's less of an issue for me.