I know there are calculators out there all over the internet, firewire surfboards…lost…etc… But what is the math behind it? Is there an equation in which I can physically (old school paper and pencil method) plug values in to find out what volume would be best for a surfboard based on a riders surf style and weight?

Let me clarify, Id like to add the metric of weight of surfer,

I am no math whiz but I can calculate the volume etc, but how does one match this calculation up so say… if I know a surfer of x weight, how much volume would they need under them to float them in stationary water (i know it doesnt apply as much for a board in motion as it is then a planing surface and hence subject to different forces)

Surfboards are not intended to float anyone in “stationary water”.

The ideal volume for two guys who weigh exactly the same can vary greatly. You are trying to quantify an intangible. Surfing is a selfish, hedonistic pursuit, not a math problem.

The buoyancy force is equal to the weight of the water displaced.

So if the board is completely submerged then the buoyancy equals the volume of the board times the weight of seawater which is around 1.027 kilograms per liter.

I used to try to figure out dimensions mathematically, and it never really worked out. The only way I found to compute volume, is to ride a board, and then make it thicker/thinner and/or wider/narrower, etc. based on how it a-paddled b-floated and c-rode. In my opinion, that’s the only want to get a dimensioned board dialed in. Also, I rarely mess with length, as that always changes the ride.The surf style of the surfer will probably dictate the design more than the weight.

I use the same guideline I’ve used since 2006, when Firewire and Lost hadn’t even started talking about volume. Those companies were all late to the party but they make up for it now by putting stuff on their websites.

.50 cubic feet per 100 lbs of body weight, for fit surfers on hpsb. Plus or minus 10% for personal preference.

.75 per 100 lbs seems to work for hybrids, 1.00 for mid lengths.

If your hws is noticeably heavier than a conventional board, you could adjust volume up just a bit. But if its a big board I wouldn’t worry about it. Dialing in volume is much more critical in shortboards where you’re generally trying to find the bare minimum that the rider can get away with; in order to get a more sensitive and submissive board.

1.25 cu ft per 100 lbs is a good general rule for longboards, maybe just a little more for old school. But not all old school were chunky, some of the most bladed longboards I’ve ever seen were Fryes from 66-67.

I think the online volume calculators are based around weight in kilo x .35 to give volume in litres for a good surfer on a hpsb.
Theres a few threads on this stuff.

Ha, I did the firewire one. I’m 21, but really short and skinny, so 120lbs. I put inter/adv as skill, excellent fitness (hooray for being young) and it gives me 13 to 14 liters… Doing the same at intermediate skill and average fitness gives me 16-18 liters. Would the board be like 1" thick or what? But I believe the .5 cu ft/100lbs would return a similar number? .5 for the 100 and .5/4 or .125 for the 25, for .652 total cu ft which is 17.7 liters.Am I missing out by not riding such little boards or something?

They have board volume as a function of 4 variables, skill, fitness, age and weight. I suppose you could obtain some of their values at specific points and fit an equation. Which would be sort of annoying to do with 4 variables.

But I’d say don’t bother and just take note of what you last rode, or go with the smart people’s recommendations posted above. I’ll stick with my short, wide and somewhat high volume (apparently) for now. It suits my style.

Wow that’s thin. I’ve been riding my 5’4"x20.75x2.25, but it’s quite thick everywhere and it’s rather rectangular. And the error on my thickness measures makes the actual measure rather worthless. I need to make/acquire a proper tool for that. 17.25" tail, like 15.5" nose. Super loose and fun, like a skateboard.

Athough, I don’t have a typical hpsb. Aka, I now have a reason to make a 5’6"x18.5"x2 something. All in the name of experimentation after all, therefore spending money is justified. I haven’t ridden a skinny board in a while. Winter project…

5’11" x 19 1/4" x 2 1/4" (25.5 Liters??? is my math correct?.. (1/2(lwh)) / 60.02 = 25.54 L was the smallest board I have ever rode, It was a surf prescriptions shortie and i think it was just too small for me, I like the 5’ 4 3/8"x20 1/4" x 2 1/2" (28.87 Liters) was muccccch better for me than the surf prescription I think the extra 3 liters makes a bigggg difference!

Re: checking out firewires or any other calculators numbers. i have tried but they have their cgi-bin password protected and hence all their calculations are hidden

Thank you so much for all of your input! I learn something new with every post I make here!