Find your board volume in litres, based on your weight and how you actually surf
The answer is a range. Its width is how much the published charts disagree about you.
A 7.2 L spread — the sources disagree by 22.2% at this point.A two-slider calculator would hand you a bare 32.4 L, without saying the number carries that margin.
None of the volume calculators floating around the web tell you where the number came from. This one does. Here is the method, the sources with access dates, and — more unusually — what we decided not to calculate, and why.
For a given weight and level, each source publishes its own litres-per-kilo figure. We do not pick one and we do not average them: the range runs from the lowest to the highest published value. When the sources agree, the range is narrow. When they disagree, it is wide — and you get told, instead of receiving a number that pretends the disagreement isn't there.
Exactly one adjustment sits on top of that envelope: board type multiplies the whole range. Nothing is added on top.
The bar is deliberately restrictive: shapers, manufacturers or established surf media only. A generic SEO calculator never counts as a source, even when it agrees with the others — citing it would be laundering authority.
| Source | Role | Accessed |
|---|---|---|
| Firewire + Rusty rustysurfboards.com | Base. Counts as one source: they publish the same chart — checked point by point across the 19 shared weights, differing by +0.001 in 18 of them, which is rounding. | 2026-09-10 |
| …Lost / Mayhem lostsurfboards.net | Base. Publishes ranges per level, plus the real board volumes of named professional surfers — which is what makes external validation possible. | 2026-09-10 |
| NSP nspsurfboards.com | Base and board type. Formula stated explicitly in the page's own code. | 2026-09-10 |
| JS Industries jsindustries.com | Not in the calculation. Cited as evidence: its formula has no neutral state — the lowest wave factor it publishes is already 1.1 — and it is also where you can see an age coefficient that exists in the code and is never applied. | 2026-09-10 |
The sources use different labels. Firewire publishes five; …Lost describes profiles in full sentences; NSP uses casual, intermediate, experienced, pro. Aligning them is a modelling decision we made, not something any source publishes.
We aligned by the semantics of the published label, never by proximity of value. Aligning by value would be circular: it would pick precisely the mapping that makes the sources agree, narrowing the envelope artificially.
Direct consequence: two levels are covered by only two of the three base sources. Their range comes out narrow for lack of evidence, not for abundance of agreement. In the calculator those ranges are hatched, with the source count in plain view — so narrowness is never read as certainty.
| Dimension | Why it's out |
|---|---|
| Age | JS Industries is the only shaper that defines an age coefficient — and never applies it. The comment next to it literally says "adjust these values as needed". Firewire had age in an older version of its calculator and removed it. |
| Wave and wetsuit | They were in the calculation until 2026-09-10 and came out when the maths was checked against a real board volume. Adding them inflated the result by 21% over a baseline that was already accurate to 1.1%. The reason is double counting — see the note above. |
| Height | NSP collects height in its form and uses it nowhere in the formula. No other source quantifies it. |
| Gender | Only JS quantifies it, at a 2% spread. Single source, no corroboration, and the difference is smaller than the envelope's own noise — which reaches 22% for an intermediate. |
…Lost publishes the real board volumes of five named professional surfers along with each one's coefficient. We ran all five through our engine, deriving the level from the coefficient Lost itself publishes — all five landed inside the range.
The warning that is missing everywhere else: these numbers are industry convention, not peer-reviewed science. There is no peer-reviewed literature on surfboard volume coefficients. What exists are charts manufacturers publish from their own experience — and which, as you just saw, disagree with each other.
Use the range as a starting point for a conversation with a shaper, not as a verdict. Someone who knows your surfing and your local waves will decide better than any chart.