Boarding School: Volume

Stu Nettle
Design Outline

By Cory Russell

In the last few years I've watched the popularity and importance of volume measurements for a surfboard reach extreme heights. While I agree that volume has a place in surfboard design its importance has been oversimplified and misused by many surf shops.

In its simplest form the volume measurement of a surfboard merely explains how much of the board is underwater when you lay on it. There's no reference to where the volume is situated, such as the nose, middle, tail or rail. Volume measurement can be used as a guideline but the other elements of the board are more important.

I've even had people try to order boards by their volume. To these people I explain that I can achieve that volume in many different ways - some will work for them and some won’t. 

The take home message is simple: Don't get obsessed with a volume measurement!


In years gone by volume measurement didn't exist for surfboards and a surfer would rely on the advice of a shaper. The introduction of computer aided design allowed the calculation of volume and if used correctly it can be a valuable new dimension.

The truth is, many, if not most, shapers couldn't calculate a surfer’s ideal volume by relying on previous board volumes. The ideal volume for a surfer can be a difficult thing to specifically calculate and on top of usual factors such as weight, age, etc., you must take into consideration the climate where they surf and the types of waves ridden. In its most simplistic form each 2.75kgs of bodyweight requires 1 litre of volume.  

In scientific terms, buoyancy - also known as up thrust - is an upward force exerted by a fluid that opposes the weight of an immersed object. If the object’s density is greater than that of the fluid in which it is submerged, it will tend to sink.

There are two main types of foam currently used to build surfboards: Polyurethane (PU) and Expanded Polystyrene (EPS). Within these two types of foam there are various densities available but I will concentrate on PU, which is the industry standard.

The weight of standard PU foam is approximately 36.86kgs per cubic metre. The weight of standard EPS foam is approximately 33.65kgs per cubic metre. According to Archimedes principle the weight of an object directly affects its buoyancy even if the volume is the same. This means that the 9.5% difference in weight between PU and EPS does affect the buoyancy of a surfboard.

Volume calculators are a dime a dozen. I'm sure many of you have entered your details into various calculators only to arrive at very different results. Often the reason for this is the ambiguous terms they use: Beginner; Beginner/Intermediate; Intermediate; Intermediate/Advanced; Advanced

Can anyone decipher the difference between these levels of surfing? For instance, when does a surfer go from a beginner/intermediate to intermediate? I suspect everyone’s description would be different and unfortunately it will affect the result a person will get.

Another flaw of many volume calculators is the five year increments for age or five kilogram increments for weight. What happens if you are in the middle and forced to choose? One volume calculator tried to take it to the next level and added a ‘Guild Factor’…what the hell is a guild factor and how do I accurately determine mine? Further investigation found more vague descriptions ensued followed by large paragraphs of jibber jabber.  

A few years ago I developed my own volume calculator to specifically avoid ambiguous terms and focus on four specific pieces of information:

The surfer’s weight.
Their age.
The average number of times they surf per week.
And how many years have they been surfing.

I calculate a specific volume amount and establish a range which is ‘+’ and ‘-‘ 1.5 litres.  After this is done I then discuss the climate where they live and waves they surf to get a more accurate result. I don’t claim to have the perfect volume calculator but at least my customers can answer the questions easily and accurately.

For those surfers that have identified their ideal volume you need to understand that this amount changes depending on the type of board you have. For example, the volume you would ride in a shortboard is different to the volume you would ride in a step up. I have developed the following guide for those obsessed with volume:

Groveller - add 9% volume
Step down - add 3% volume
Step up - add 5% volume
Semi gun - add 15% volume

Keep this in mind when you are ordering a new board and it will allow for the necessary increases in a board’s dimensions.

Cory Russell
Cory Surfboards / Stretch Boards Australia

Wanna read past articles of the Boarding School?
Bottom Curves Part 1
Bottom Curves Part 2


goofyfoot's picture
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goofyfoot commented Monday, 10 Apr 2017 at 4:11pm

Love these articles.

SHARKMAN the legend will be along any time now

OHV500's picture
OHV500's picture
OHV500 commented Monday, 10 Apr 2017 at 9:05pm

Great Article Cory - well done !!!
Finally - the heads-up on volume. Basicly I reckon its a hipster measurement. Never have I ordered a board with volume in mind (maybe I'm old school). If you have a good relationship with your shaper, leave it to him :)

cgrover's picture
cgrover's picture
cgrover commented Monday, 10 Apr 2017 at 5:02pm

Thanks for the article, really interesting. You make mention of age as a determinant in the calculations and I think this is the great unknown in many of the calculators. One of the things we all see is that as surfers get older they more often than not ride longer, wider and thicker boards and the capacity to paddle harder for longer. In the last few years i have increased my volume, especially in my grovellers and fish and have improved my wave count without too much noticeable change in performance. I make use volume (it isn't a hipster measure rather a useful guide), but length, width, thickness, plan shape and foil are still the most important measurements in selecting any board.

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming commented Monday, 10 Apr 2017 at 6:41pm

Although i agree there is now people who rely on the volume measurement to much these days thinking it's the be all and not understanding other design elements etc

Im a huge fan and believer in the the volume measurement, Actually in the early 90's I remember saying to my local shaper how cool it would be to have this measurement and he said yeah it would, but he is not going to waste his time with some tank to measure boards. (obviously before CAD was around or used much for surfboards)

People can ignore how useful the volume measurement is, call it hipster etc, but IMO smart surfers use any info they can to get a good board and the more info you have the better.

Heres a few reasons i believe it's useful.

1. Once upon a time in everyday conditions we all rode basically the same board all the time like a 6,3 x 18.5 x 2 1/4 and we knew our ideal volume or just let our shaper do his work.

Now many of us ride and have quivers of all kinds of boards of all kinds of shapes widths, thickness, bottom shapes, it can be extremely hard to know how far you can push things, how short you can go without going to low in volume, or you also don't want to go to high in volume.

2. Shapers are so clever these days in hiding volume in different areas of the board and it can be deceptive volume is good as a reassurance or a starting point.

3. people change overtime, we often put on or take off weight, or go through stages ion different fitness levels or both of these due to age, knowing volume of you boards is helpful and keeps things realistic. (although i think most volume calculators etc are wrong, IMO you just need to find your ideal volume for different types of boards yourself)

4. Possibly more than ever surfers are grabbing boards of the rack, so the more info and knowledge you have about a board the better as you are not relying own the shaper to get the board you need.

All that said for most surfboard designs volume is not all that important when up and ridding and on a plane, its more about paddling, maybe the only time you want more volume for actual surfing is for a grovel type of board where you are often not planning at speed and extra volume is an advantage .

Then to add to that three different boards of different designs but the same volume can paddle completely different due to other factors, like length, width, rocker, bottom shape and how the foam is distributed, so design elements need to be taken into account.

Im glad the article touch on foam distribution because I've though about this and id love to see the volume measurement go a step further and be broken up into either a half or two thirds measurement to show where the volume is in a board, for instance instead of just 30L id love to see the board divided in half as 30L @ 13/17 which will then show from a measurement where the foam is in a board. (or one step further 30L @ 9/13/8

I totally disagree with the EPS v's PU foam paddling thing, i really really wish it was true it would be great if i could ride a EPS/Epoxy board of less volume while it floating the same as a PU/PE board of a higher volume, but in my experience is not noticeable and if its all about weight not all epoxy/EPS boards are lighter than PU/Poly boards as we know PU/Poly board vary quite a bit in weight due to foam density and obviously the glass job.

BTW: Personally i ride my grovel boards about 30-31L, my everyday boards about 29-30L and often my indo boards 27-30L as i dont have thew weight of a wetsuit in Indo and many waves i surf don't have a rip of current to paddle against and i often want my boards more refined and lower in volume.

Ada gula, ada semut!

cory's picture
cory's picture
cory commented Monday, 10 Apr 2017 at 9:56pm

Hey Indo Dreaming,
You are spot on when you talk of dissecting volume. Length, width and thickness are defined and measured in a way that cannot be challenged. A volume amount is very ambiguous and can be manipulated in so many ways.
Given the level of ambiguity it undermines the importance of volume unless a person is riding the same model with the volume distributed in the same place.

In regard to EPS vs PU... it's all factual information based on real data. 'How a board feels' is an emotional response and often something which cannot be measured.

Thanks for sharing your thoughts and ideas :)

indo-dreaming's picture
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indo-dreaming commented Tuesday, 11 Apr 2017 at 8:05am

Im still sceptical :)

Ada gula, ada semut!

Lanky Dean's picture
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Lanky Dean commented Tuesday, 11 Apr 2017 at 2:11pm

"You are spot on when you talk of dissecting volume. Length, width and thickness are defined and measured in a way that cannot be challenged. A volume amount is very ambiguous and can be manipulated in so many ways.
Given the level of ambiguity it undermines the importance of volume unless a person is riding the same model with the volume distributed in the same place."

Totally agree with both of you about this. plan shape also plays a big factor in buoyancy / up thrust. Never had a board with a volume measurement.

nicko74's picture
nicko74's picture
nicko74 commented Monday, 10 Apr 2017 at 11:30pm

I have only noticed volume on boards for the past 5 or 6 years. I only now use it as a guide if anything. IMO interpreting the dimensions should give most punters an idea of the boards purpose. My gun/step up only has a little more volume than my go to all round shorty, Just more refined, longer and pulled in. Great article.. speaks volumes:)

rooftop's picture
rooftop's picture
rooftop commented Tuesday, 11 Apr 2017 at 1:27am

So, in manufacturers' efforts to better communicate the complex art of board design to the average punter we've ended up with the reductio ad absurdum being board volume.

You can criticise it for being simplistic and reductive, but is there any other single metric that better describes a board? Along with a pic of the outline and the length, it tells most people at a glance the most essential information they need, doesn't it?

Of course it falls far short of building a relationship with a shaper, doing your homework, and riding a bunch of different types of boards. But nobody can argue that it doesn't play a helpful role in board selection, especially in designing a board selection algorithm to help the uninitiated or the online customer.

You realise I'm just making this up and have zero actual industry experience, right?

Anyhoo, Cory offers an interesting series of inputs for a board selection formula. Does anyone else have any other key inputs they would recommend? Or a better interface for simplifying the dark arts of board design for the neophyte? Might be a pretty penny in that.

indo-dreaming's picture
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indo-dreaming commented Tuesday, 11 Apr 2017 at 8:12am

I think that is 100% true if there was only one measurement you could use to buy a board and you could not physically pick up and check out the board volume would be the most useful measurement.

I think that's why many don't like it, because i guess it has opened up a market for people to buy or order online boards online, its a measurement that doesn't give much advantage to smaller shapers, but does to bigger board labels.

Ada gula, ada semut!

Island Bay's picture
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Island Bay commented Tuesday, 11 Apr 2017 at 1:56am

You forget that it's not just the weight of the board trying to displace the volume of water, but the combined weight of board and rider. And two boards with identical volumes will displace the same amount of water.
Working against that is the weight of the board plus rider.
And even without the rider's weight, there is precious little difference; let's say the PE board weighs 3kgs, the PU 4kgs. They both have a volume of 30L. The difference in displacement will be 1L (4kgs minus 3kgs), that's only about a 3% difference in buoyancy. Without accounting for the surfer's weight.

The main difference is in feel, not in actual numbers.

indo-dreaming's picture
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indo-dreaming commented Tuesday, 11 Apr 2017 at 8:17am

I agree

Ada gula, ada semut!

cory's picture
cory's picture
cory commented Tuesday, 11 Apr 2017 at 10:10am

Hey Island Bay,
I totally agree displacement plays an important part in all of this. That is why I regularly have people say to me how much better/worse and EPS board might paddle for them when it's a completely different board. I asked Stretch why he has not followed the trend and put more volume information on his website/boards? He told me... 'all it tells you is how dry your titties are when you paddle!' He was over simplifying things but he was pointing out the different benefits of volume distribution for paddling compared to surfing. Cheers :)

Island Bay's picture
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Island Bay commented Tuesday, 11 Apr 2017 at 2:46pm

Stretch may shape good boards (never ridden one), but I have always had a had time making sense of what he says (spherical rocker - huh?).
Yes, length and surface area play a huge part, but try paddling an alaia; it ain't easy. Volume is your friend, and it's a good number to know - but not to live by.

roubydouby's picture
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roubydouby commented Tuesday, 11 Apr 2017 at 5:14am

Perhaps a volume by thirds metric would be useful.
I've definitely been guilty of using volume as a guide only to find 3 boards of the same volume that paddle vastly different.

Results may vary.

cory's picture
cory's picture
cory commented Wednesday, 12 Apr 2017 at 7:38pm

Hey Roubydouby,
That could be an option but then it fails to identify the volume in a surfboards rail or perimeter. The amount of volume in the rail plays a massive part in how easy or difficult it is to submerge the rail. Cheers :)

roubydouby's picture
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roubydouby commented Thursday, 13 Apr 2017 at 12:25pm

Isn't the issue then that all the standard metrics given are too vague to really define the nuance of a board?

I know they are reductive, but if you could put an 'ideal' set of variables on a board what would they be?

Results may vary.

cory's picture
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cory commented Thursday, 13 Apr 2017 at 12:40pm

The current measurements are fine and that includes volume. I just get frustrated when surfboards are pidgeon holed solely on one measurement. Surfboards are not T shirts and will never be reduced to Small, Medium, Large and Extra Large. People should be excited to talk to a shaper/s and get the right board for them not necessarily what their favourite Pro is riding. I fear a lot of the 'top' shapers could not even calculate someone's volume.

OHV500's picture
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OHV500 commented Thursday, 13 Apr 2017 at 5:01pm

"people should be excited to talk to a shaper/s and get the right board for them not necessarily what their favourite Pro is riding." - Totally, totally agree

bean's picture
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bean commented Tuesday, 11 Apr 2017 at 2:28pm

If it feels good under your arm then you know it'll work..

Goodwolf's picture
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Goodwolf commented Tuesday, 11 Apr 2017 at 11:30am

Registered just to say thanks for the great article Cory. As one who regularly and unwittingly slides in to hipsterdom, it's great to get a nuanced view of volume. Could have done with that calculator years ago!

cory's picture
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cory commented Tuesday, 11 Apr 2017 at 4:11pm

Thanks Goodwolf! My main motivation for these articles is to provide information and encourage people to start a relationship with a shaper. Thanks for the feedback. :)

MRsinglefin's picture
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MRsinglefin commented Thursday, 13 Apr 2017 at 5:24pm

Totally agree about the calculator years ago.
Thornton Fallander's has always said "Foam is your friend"

indo-dreaming's picture
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indo-dreaming commented Thursday, 13 Apr 2017 at 3:08pm

@ Cory generally when surfboards come with a litre measurement they have obviously been designed on a CAD type program and then cut by machine, then finished off by hand.

So obviously if the machine cuts a blank and it's 30L then it's tidied up by hand how much foam is removed? Is it enough to say make the board end up being 29L for example?

Ada gula, ada semut!

udo's picture
udo's picture
udo commented Thursday, 13 Apr 2017 at 3:43pm

Remove all cutting ridges top and bottom ..shape the rails and add a bit more concave here and there and a all round tidy up of the shape would be up to a litre loss for sure.
Cut in a deep swallow tail..whats that 1/8 or 1/4 of ltr foam loss ?

philosurphizingkerching's picture
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philosurphizing... commented Thursday, 13 Apr 2017 at 4:28pm

It would be good if a designer who has the skill to use one of the CAD type programmes could give some examples of how volume numbers change when you play around with aspects such as thickness, length, deck roll, position of wide point etc.
For example someone on Swaylocks asked what the volume increase would be if a 5' 8'' boards thickness was increased by 1/8'' from 2 3/8'' to 2 1/4'', the answer was 1.6 litres, which means a 1/4'' increase would increase the volume by 3.2 litres and a 1/2'' increase 6.4 litres.

simba's picture
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simba commented Thursday, 13 Apr 2017 at 5:42pm

Volume increases way more with thickness than width or length.You can see this for yourselves on the channel islands volume calculator on there site,just play around with a board and see how much difference there is with adding thickness more so than width or length.


udo's picture
udo's picture
udo commented Tuesday, 13 Mar 2018 at 12:56pm

U want Volume ?
How about a 11'6 x 22 1/2 x4 1/2 - 125 litres weighing in at 15kgs
Dylan Longbottom gun for nazare

Blowin's picture
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Blowin commented Tuesday, 13 Mar 2018 at 1:11pm

Clay Marzo’s board in his new clip : 6’2 * 19 1/2* 2 9/16

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