How much volume should a fish have?

Keiller · October 3, 2026

If you read my first post, you know I started surfing fishes kind of by accident. I bought a 6'2 Rusty Dwart off Facebook Marketplace thinking it was going to be my step-up for Ocean Beach, and it took a better, more seasoned surfer calling it a fish for me to figure out what I actually had. Since then, one question I keep coming back to is how much volume a fish should actually have. Spoiler: probably more than you think.

Why fish feel different

Fish are usually shorter, wider, and flatter than a standard shortboard, with a wide tail (a lot of the time a swallowtail) that helps them hold speed in small, weak waves. All that width and flatness is where the extra foam comes from, and it's why a fish can feel way floatier than its length would suggest. The Dwart is 6'2, but at 39 liters it paddles nothing like a 6'2 shortboard would.

My numbers

My Hypto Krypto is a 5'8 at 31 liters. The Dwart is 39. I'm 160 lbs, which is about 73 kg, so that works out to a Guild Factor of about 0.43 on the Hypto and about 0.54 on the Dwart. That's 8 more liters, or roughly a quarter more foam. On paper that sounds like a lot. In the water, on a typical closeout day at Linda Mar, it's the difference between sitting around for 30 or 40 minutes and actually getting waves.

So how much volume should your fish have?

There's no magic number, but here's how I'd think about it:

Start with your shortboard number. If you don't have one, the Setwave calculator will give you a range.
Go up from there, not down. A lot of people ride their fish a few inches shorter than their shortboard, but because fish are so much wider, they usually end up with the same volume or more. If you're getting a fish for small, mushy days, a few extra liters is a pretty safe bet.
If you only surf on weekends, lean toward the high end. I went up 8 liters and I haven't regretted it once. Being able to take off a bit earlier and have a split second longer to set my line has done more for my surfing than almost anything else.
Know the trade-off. The more foam you have, the harder it is to duck dive. I can't get the Dwart under a set the way I can with the Hypto Krypto, so if your break has a long paddle out on bigger days, keep that in mind.

That said, a fish isn't just a small-wave board. On a recent trip to Maui, I was surfing some hollower waves and I still took my fish out, because I could take off a bit earlier and set my line. For a surfer like me, that's a lot more doable than taking off super vertical.

The homies might give you grief for riding a fat little fish, but a fish is supposed to be fun. More waves = more fun.

If you want a starting point that's actually built for you, put your weight, how often you surf, and the waves you ride into the Setwave calculator, then add a few liters from there for your fish.

Calculate my volume