How we calculate your board
Litres = weight in kilos × level factor, corrected for age, frequency and wave type. The factors run from 0.85–1.0 for someone starting out to 0.28–0.35 at expert level, and they are calibrated against the industry consensus rather than invented.
The formula and the factors
The base was set by Whitney Guild with the Guild Factor: one litre floats one kilo, so the volume you need is your weight times a coefficient that drops as you improve. It is the framework behind the Global Surf Industries and Lost calculators and most brand tools, with variations in the coefficients.
| level | L/kg | Band | Recommended |
|---|---|---|---|
| beginner | 0.85 – 1.00 | 68–80 L | 78 L |
| improver | 0.55 – 0.68 | 44–54 L | 52 L |
| intermediate | 0.42 – 0.52 | 34–42 L | 38 L |
| advanced | 0.36 – 0.44 | 29–35 L | 32 L |
| expert | 0.28 – 0.35 | 22–28 L | 25 L |
The modifiers
Age: three litres are added per decade above 40. It is a standard adjustment among shapers and it reflects the loss of explosive paddling power, not general fitness.
Frequency: surfing three or more times a week drops it eight per cent; surfing a couple of times a month raises it seven. The paddle that counts is the one you have now, not the one you used to have.
Wave type: it decides where in your band you land. Soft waves push you to the top, walled waves to the bottom, and big waves step outside the range with an extra twenty per cent, because there the goal is to get in early and in control.
From volume to an actual board
With volume settled, the shape follows from your level and your waves: softboard to start, mid-length while progressing, fish for small days, hybrid as the middle ground, shortboard for walled waves and gun for big ones. Length is derived from your height and clamped to the shape's limits.
Then width and thickness are solved so the volume adds up, using that shape's fill factor. If it does not add up, the board grows in length within its range first, and if it still does not fit, the shape changes. Dimensions that do not match the volume are never shown: the number you see always comes from the dimensions you see.
Where we differ from the consensus
In July 2026 we recalibrated the bands downwards. The previous version gave roughly 62 litres to an intermediate of 165 lb (75 kg), when the consensus across sources sits between 31 and 39. The bias came from applying the beginner's safety margin to every level.
That pro-volume bias is now reserved for people genuinely starting out or improving, which is where the typical mistake is buying too small. From intermediate upwards the recommendation lands in the middle of the band, or below it when the waves have power.
| Source | Intermediate factor | For 176 lb (80 kg) |
|---|---|---|
| Guild Factor | 0.50 – 0.60 | 40 – 48 L |
| Global Surf Industries | ≈ 0.40 (experienced) | 32 L |
| Singlequiver | 0.40 | 32 L |
| Magicwave | ≈ 0.82 | 66 L |
| This calculator | 0.42 – 0.52 | 34 – 42 L |
Sources
- Guild Factor, by Whitney Guild — The original framework: weight times a skill coefficient.
- Global Surf Industries — Reference coefficients by level, from beginner to pro.
- Lost Surfboards — A brand calculator built around a high-performance range.
- Mundo Surf — Beginner ranges as used in the Spanish market.
- SurfSpotGuide — Bands by level and wave type.
What this calculator does not do
It estimates. It does not replace a shaper who has watched you surf, or borrowing a friend's board, which is still the best way to know whether a volume suits you. It does not account for rocker, foil distribution, fin setup or the particular wave at your spot, and all of those move the feel as much as a couple of litres.
It also cannot tell whether your problem is the board or your technique. If you are not catching waves and your volume is in range, the missing litre is probably in the paddle.