Surfboard volume calculator: the right litres for your weight and ability

26.3 litres or 52.5: for a 75 kg surfer, Firewire’s chart doubles the volume of a board from one end of the ability scale to the other [1]. The tool above makes that chart usable at any weight; what is left is to find out what its answer is worth. Let’s do the sum.

What the tool calculates

The tool guesses nothing: it reads Firewire’s volume chart, which gives one volume per weight and per ability level, from advanced to beginner [1]. Between two rows it interpolates in a straight line. For 75 kg at intermediate level, the default values, it lands on a row of the chart: 32.8 litres, or about 0.44 litre per kilo. For 70 kg it joins the 68 and 75 kg rows and shows 30.7 litres.

Over the usual range, 59 to 91 kg, the chart amounts to multiplying your weight by a coefficient: about 0.35 for an advanced surfer, 0.37, 0.44 and 0.53 for the in-between levels, 0.70 for a beginner [1].

The coefficient moves at the extremes

Outside that range the coefficient changes. Firewire’s full chart goes down to 36 kg (80 lb) and up to 109 kg (240 lb): an advanced surfer of 36 kg is given 16 litres, or 0.44 litre per kilo; at 100 kg, 36 litres, or 0.36 [1].

Enlarge diagram

The tool has only five rows, from 59 to 91 kg. Below and above them it scales proportionally to weight, which amounts to keeping the coefficient of the outermost row. Its result then drifts away from the full chart:

The gap runs from 1.1 to 2.9 litres in these three examples: below 59 kg and above 91 kg, Firewire’s chart is the reference, and the tool comes out a little low.

Firewire and Lost: two scales that part ways

Firewire’s chart is not the only reference. Lost publishes a guild factorThe ratio of a board’s volume, in litres, to the surfer’s weight, in kilos; Lost’s calculator credits it to Whitney Guild, in 2013. for each type of surfer, for shortboards only: 0.34 to 0.36 for an advanced, very fit surfer, 0.36 to 0.38 for average to good fitness and ability, 0.38 to 0.42 for the weekend surfer, 0.40 to 0.50 for a novice or in tough conditions [2].

Enlarge diagram

At 75 kg that gives 25.5 to 27 litres at Lost for the advanced surfer, against 26.3 at Firewire: the two agree. Then they drift apart. Firewire’s beginner, 52.5 litres, is 15 litres above the top of Lost’s range for a novice, 37.5 litres [2]. Lost keeps its ratios for shortboards; a beginner on a bulkier board falls outside them.

What the figure cannot know

Conditions shift the result. Lost recommends the low end of its range in warm water and good waves, the high end in poor conditions, in a crowd or in a thick wetsuit [2]. The French Surfing Federation points out that a wetsuit protects against the cold and gives better buoyancy [3].

More volume also makes paddling easier. In a 2017 study, twenty surfers paddled in a swim flume on five boards that differed only in thickness, from 28.4 to 37.4 litres: on the thicker ones, oxygen consumption and heart rate fell, as did pitch and roll [4]. The study measures paddling, not how easily a board turns: it does not say how far to go.

Finally, there is the water. According to NOAA, seawater averages 35 grams of salt per litre, from 33 to 37 depending on the sea, and its density rises with salinity and as the temperature falls [5]. The same board therefore carries a little more in cold, salty water than in warm or fresh water. We do not put a figure on this effect: keep the direction, not the value.

From the figure to a board

What is left is turning litres into a size. Torq’s spec sheets publish the volume of every size: for 32.8 litres, these are the closest [6] [7].

At 5’8 the PG-R holds 32.2 litres and the Summer Fish 34.4: a 2.2-litre gap at the same length, which no length would let you guess. Compare the litres on the spec sheets, not the feet.

For a beginner, the tool’s result is not the size of a foam learner board. The French Surfing Federation advises starting on a foam learner board [3]; at Torq, the soft-deck longboard is listed at 66 to 95 litres [8], well above the 52.5 litres of our 75 kg example. For those boards, read the volume on the model’s spec sheet.

For shapes and conditions, see our guide on surfboard volume; for cold water, wetsuit thickness by water temperature; for your first session, the beginner’s guide.

The rule fits in one sentence: work out the volume, pick the board that comes within a few litres of it, then judge it in the water rather than on paper.

Worth watching

Surf Simply’s animated series shows how an online calculator links weight to volume through a ratio, an 80 kg surfer on a 40-litre board being at 50%, then how to place yourself on its level system.

The video is hosted by YouTube (Google): nothing loads until you play it, and Google may then set cookies.

Julien de Jurquet

Campervans, motorhomes, cycling and calculators

Julien de Jurquet writes for Outfarer about campervans, motorhomes, cycling and calculators. He reads instruction manuals to the very end and never lets a figure through without its unit, so that your choices rest on sums rather than promises.

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