Calculating volume

Been shaping a while now and people always ask me the volume and not confident I’m giving the right answer. Been doing length x width x depth x board type factor / 1000. Board type factor is where I’m not sure if I’m correct. Found could be anywhere between .54 and .6

I always use this website

Cheers and good waves.

Just tell them whatever they want to hear. Volume is for machine shaped boards and the volumes written on the bottom of machine shaped boards are still just a guess depending on what the guy did who finished shaping the board after it came off of the machine.

I agree. People get way too hung up on it. So much more goes into a good board than people realize.

I’ve started calculating volume by weighing and measuring foam.

For your starting block of foam, measure L X W X H in meters and divide by the weight of the block in kilograms. EPS is around 17 kg/m3 so your answer should be in that range.

Weigh your shaped blank in kilograms and divide by your measured kg/m3 from above (e.g. 17).

A blank that weighs .850 kg, divided by 17 kg/m3 would calculate to .050. Multiply by 1,000 and you get 50, which will be the volume in liters.

If your board has a stringer, weigh your stringer separately and subtract that from the overall board weight. The stringer will add a bit of volume but because it will weigh more than foam your most accurate calculation will come from using just the foam weight. The blank also has to be weighed before adding anything other than foam (e.g. fin boxes).

Oops, I just reread after posting. The second paragraph is backwards. Weigh the block of foam in kg and divide that weight by the cubic meters of the block (L X W X H) to get kg/m3.

This is interesting the answers you read
Take into account the experience and weight of the owner and remember that displacement of a human body is not by volume.
The same hold true for materials used, glass weights, resins, number of fins type of boxes , or glass- in fins.
I’ve been riding boards from the beginning were only floating me chest high in the water when sitting.
The ocean has a basic salinity, that different water temperatures vary now the popularity of fresh water pools there is a totally different set of calculations.
Now if you want to figure in velocity and volume of the wave ridden the depth and type of break then those calculations in my opinion matter the most.

Much higher effort but could help confirm your shape factors by just measuring it directly on the finished board:

  1. Get a trash can that’s at least half the board’s length and that you can put the board in
  2. Fill trash can with water
  3. Submerge board to half it’s length or more and mark furthest up the board the water level gets, with a line or with two dots.
  4. Remove surfboard from water and trash can.
  5. Take a gallon or liter jug, fill it and then pour in the trash can to refill. Repeat until the trash can is full again, counting how many gallons or liters it takes to refill.
  6. Flip the surfboard over and submerge again to the place you marked last time. For example if you started by submerging the tail and have a mark around where your front foot would go, now you’ll submerge it nose first up to that mark.
  7. Remove the surfboard and repeat the refill process measuring as you go.
  8. Add the amounts of water it took to refill the trash can each time and that’s your finished surfboard volume either in gallons or liters (1 gal = 3.785 L).
    If you want to be quite precise use a liter jug that has markings on it, at least for the last dump in to fill the can. Otherwise just estimate how much is left in the last gallon/how much your poured in.


Welcome to the forum Lambyr.

If I need the volume of something, I typically rough it into CAD and question the software or for a board, into a shaping program where it shows up right next to the other main dimensions.

Weighing foam after shaping and doing it as a density problem works too, if you know either the actual foam density or the volume. My latest pre-shape weighs 2.696#, the volume is 1.833 CF (51.9 L) according to CAD, indicating foam density around 1.47 PCF which is plausible for 1.5 PCF nominal foam.
If I go the other way, 2.696# (weight)/1.47 PCF (density)=1.834 CF (volume estimated)

My quick estimate for calculating approximate volume.