Simple question but one I've never asked....Is the weight of the board included in the volume...such as an 87ltr wave board that weights 7kg...is really 94ltrs but the 7kg takes it down to 87ltrs or is it 87ltrs but with 80kg float....I'm guessing its the former but I've never heard it mentioned - thx
I think it's neither. Volume is volume. Weight is weight. Float depends on the density of 'ether' that surrounds the board. Sail 80L board in mercury and it will be able to hold your entire family. 
It's the latter. I.e. 87 litres volume, weighing 7kg has 80 litres float. This is why we target a board with 20 litres more volume than we weigh as suitable to uphaul to account for the combined weight of the board, rig, harness and what we wear when sailing.
I agree on the neither suggestion above. :)
An 87liter board feels different i sweet-water compared to salt-water.
Historically, the volume is determined by the marketing department, not by actual measurements. That's why you'll be able to find boards of supposedly identical volume where one feels a lot bigger than the other (even if the shapes are similar).
With most shapes now being designed on the computer, that should not really be true anymore ... except that programs may just give you the volume of the blank, and you may just have to guess (or perhaps ignore) the volume that the sandwich layer and skin add. Some companies also make changes pretty late in the design cycle, for example after making hard foam modifications to prototypes during testing. Those may change the volume by a few liters up or down.
That said, the volume seems to generally indicate exactly what it says: the volume. So a 100 l board will float a total of 100 kg in fresh water, and about 103 kg in salt water. If the board weighs 7 kg, and the rig 8 kg, the that leaves 85 respectively 88 liters to float the sailor. Seems to be about right - at 85-90 kg, boards of ~ 110 l will usually float me quite easily, while 90 l boards sink.
Select to expand quoteSurferKris said.
An 87liter board feels different i sweet-water compared to salt-water.
Thats due to the SG of the liquid.
Not the volume or weight of board.
I guess the Volume vs Bouyancy numbers REALITY is up to the Manufacturer.
Whether they actually went that far with their design parameters to subtract the construction Weight from the Bouyancy value.
A Naval Architect certainly does. But does this carry thru to sailboard design???
Back in early 2000's some boards were advertised they had XX volume but rode like a bigger volume board. Was this just the Volume vs Bouyancy game being played?
GREAT QUESTION !
The answer to the question is , volume is volume . Gots nothing to do with weight or boyancy . You can get the same board in different constructions with different weights still being the same volume .
One litre of water is one kg . That is distilled water at sea level at 4 deg from memory . So , one litre will just float one kg . Shape of board only makes things feel different.
So , the volume of the board minus its weight , minus the water on top of the board and in the straps and pads is what it should float in kg in fresh water . The water on the board and in straps only matters when the board is floating , not when under water . Add about 3% in salt water . ( it feels a lot more ).
Provided the board figures are correct .
Adding 20 litres plus body weight for uphauling is for competent sailers with good balance . If board is 7 kg , wet rig at least 7kg and wet wetsuit and harness 6 kg , that leaves nothing .
Nerd leaving the building 
At 90plus kilos plus a winter wetsuit so probably at least 100kg I can easily uphaul a 9.4 race sail on my fox 120
oh and volume is volume regardless of weight of board etc
Yes, volume is volume. But the volume isn't always the number written on the board, that is sometimes just the model number.
Select to expand quoteSurferKris said..
I agree on the neither suggestion above. :)
An 87liter board feels different i sweet-water compared to salt-water.
Well Leto's answer above explains exactly that.
Buoyancy depends on volume, weight and medium.
So if you disagree you didn't understand his answer.
Agree with, "volume is volume", I had a 180L Bic Nova with no cracks or leaks that was 30 lbs and sat low in the water because of that and when I did a tack with an 9.0 sail the nose would start to sink if I was not quick, then I got a 142L Magic Ride that weighed 18lbs and with the same 9.0 sail the nose was noticeably more buoyant during a tack. Now the Nova had a solid core, while the MR core was hollow with a vent plug and I think that and the lower weight made the MR more buoyant.
Select to expand quoteSandman1221 said..
Agree with, "volume is volume", I had a 180L Bic Nova with no cracks or leaks that was 30 lbs and sat low in the water because of that and when I did a tack with an 9.0 sail the nose would start to sink if I was not quick, then I got a 142L Magic Ride that weighed 18lbs and with the same 9.0 sail the nose was noticeably more buoyant during a tack. Now the Nova had a solid core, while the MR core was hollow with a vent plug and I think that and the lower weight made the MR more buoyant.
Yeah , naa , a Magic Ride has a solid core . Its not hollow . Not even a little bit .
Yep Volume is Volume.
But Volume does NOT = Bouyancy or 'float'.
To work out the Bouyancy you must subtract the Construction weight from the Volume capacity.
Marketing could use the volume thing for either argument to suit their needs.
Anyway
FIRSTLY WE GOTTA HAVE REAL n ACCURATE VOLUMES.
Back to the Manufacturers n Designers.
Whenever I get a new board I have a ritual. On a calm day, (wind measurement, not whether the missus has got over me secretly buying said new board) I fill the swimming pool to the brim, then I lie down black plastic right around the pool. Then I get the board straight out of the box and place on the surface of the water. Gently push the board down until the board is submerged. I funnel the water that has spilled out of the pool, on to the plastic, into a container and seal securely. Then I take it to a boutique brewery in town that gives me a very accurate total litre measurement. Whatever the number is = the volume. While I am comprehending the difference between that volume number and what is painted on the board, I have a couple of beers whilst still at the brewery. Done.
Select to expand quoteOrange Whip said..
Whenever I get a new board I have a ritual. On a calm day, (wind measurement, not whether the missus has got over me secretly buying said new board) I fill the swimming pool to the brim, then I lie down black plastic right around the pool. Then I get the board straight out of the box and place on the surface of the water. Gently push the board down until the board is submerged. I funnel the water that has spilled out of the pool, on to the plastic, into a container and seal securely. Then I take it to a boutique brewery in town that gives me a very accurate total litre measurement. Whatever the number is = the volume. While I am comprehending the difference between that volume number and what is painted on the board, I have a couple of beers whilst still at the brewery. Done.
Very elaborate process but I like it 
Select to expand quoteOrange Whip said..
Whenever I get a new board I have a ritual. On a calm day, (wind measurement, not whether the missus has got over me secretly buying said new board) I fill the swimming pool to the brim, then I lie down black plastic right around the pool. Then I get the board straight out of the box and place on the surface of the water. Gently push the board down until the board is submerged. I funnel the water that has spilled out of the pool, on to the plastic, into a container and seal securely. Then I take it to a boutique brewery in town that gives me a very accurate total litre measurement. Whatever the number is = the volume. While I am comprehending the difference between that volume number and what is painted on the board, I have a couple of beers whilst still at the brewery. Done.
Inspiring ritual! I'd love to do this, too, but since I don't have a pool, I'll have to skip straight to the last part.
Select to expand quoteSparky said..
Yes, volume is volume. But the volume isn't always the number written on the board, that is sometimes just the model number.
Had a Starboard Formula "156" with a nose like a potato chip/crisp. Actual volume stated by Starboard was something like 136 129 but this was back when Starboard was doing the virtual volume stuff to account for the fact that very wide boards with low volume feel substantially more stable than narrow boards of similar volume.
More fun and games with board models and actual volumes: ISAF approved formula list www.yumpu.com/en/document/read/36526179/isaf-formula-board-list
Last four columns, weight, length, width, volume and availability
Select to expand quoteboardsurfr said..Orange Whip said..
Whenever I get a new board I have a ritual. On a calm day, (wind measurement, not whether the missus has got over me secretly buying said new board) I fill the swimming pool to the brim, then I lie down black plastic right around the pool. Then I get the board straight out of the box and place on the surface of the water. Gently push the board down until the board is submerged. I funnel the water that has spilled out of the pool, on to the plastic, into a container and seal securely. Then I take it to a boutique brewery in town that gives me a very accurate total litre measurement. Whatever the number is = the volume. While I am comprehending the difference between that volume number and what is painted on the board, I have a couple of beers whilst still at the brewery. Done.
Inspiring ritual! I'd love to do this, too, but since I don't have a pool, I'll have to skip straight to the last part.
Try it in your bathtub! Much better controlled environment
What about displacement, a wider board will feel more stable than a narrow board of the same volume.
Select to expand quoteduzzi said..boardsurfr said..Orange Whip said..
Whenever I get a new board I have a ritual. On a calm day, (wind measurement, not whether the missus has got over me secretly buying said new board) I fill the swimming pool to the brim, then I lie down black plastic right around the pool. Then I get the board straight out of the box and place on the surface of the water. Gently push the board down until the board is submerged. I funnel the water that has spilled out of the pool, on to the plastic, into a container and seal securely. Then I take it to a boutique brewery in town that gives me a very accurate total litre measurement. Whatever the number is = the volume. While I am comprehending the difference between that volume number and what is painted on the board, I have a couple of beers whilst still at the brewery. Done.
Inspiring ritual! I'd love to do this, too, but since I don't have a pool, I'll have to skip straight to the last part.
Try it in your bathtub! Much better controlled environment
My method would be to fill the bathtub with ice and beer and try to drink it all . Board stays in the garage .
Select to expand quoteImax1 said..Sandman1221 said..
Agree with, "volume is volume", I had a 180L Bic Nova with no cracks or leaks that was 30 lbs and sat low in the water because of that and when I did a tack with an 9.0 sail the nose would start to sink if I was not quick, then I got a 142L Magic Ride that weighed 18lbs and with the same 9.0 sail the nose was noticeably more buoyant during a tack. Now the Nova had a solid core, while the MR core was hollow with a vent plug and I think that and the lower weight made the MR more buoyant.
Yeah , naa , a Magic Ride has a solid core . Its not hollow . Not even a little bit .
The gift that keeps on giving...
I have always wanted to know the true Vol of boards, some of the euro stuff (rrd) quote litres instead of volume. But really does it matter, a couple of litres either way.do they take in account for the Routing of finbox,mast insert???
Select to expand quotegavnwend said..
I have always wanted to know the true Vol of boards, some of the euro stuff (rrd) quote litres instead of volume. But really does it matter, a couple of litres either way.do they take in account for the Routing of finbox,mast insert???
Volume is measured in litres
Select to expand quoteWind Smurf said..
What about displacement, a wider board will feel more stable than a narrow board of the same volume.
Displacement is how much water it pushes out the way, nothing to do with width or stability. Long skinny board and a short wide board can have the same displacement
Select to expand quoteBen1973 said.. Displacement is how much water it pushes out the way, nothing to do with width or stability. Long skinny board and a short wide board can have the same displacement
It's a bit surprising, how many people here are mixed up about basics
Select to expand quotedecrepit said..Ben1973 said.. Displacement is how much water it pushes out the way, nothing to do with width or stability. Long skinny board and a short wide board can have the same displacement
It's a bit surprising, how many people here are mixed up about basics
And I thought we were the smart ones . Imagine how much the kiters would be struggling
Select to expand quotedecrepit said..Ben1973 said.. Displacement is how much water it pushes out the way, nothing to do with width or stability. Long skinny board and a short wide board can have the same displacement
It's a bit surprising, how many people here are mixed up about basics
people get mixed up about a lot of things, not just volume and displacement ... some people still think earth is a spheroid!!!!! Think about that! Despite all the evidence for a Donut shape!
In a spheroid world they would measure SUP board length and width with imperial sizes and volume in metric sizes just to confuse people .
I imagine volume is just volume, as in how much water would be displaced if the board was held under water. So the density/weight of the board doesn't change the volume in litres, but will affect the flotation i.e. a heavier board will float less for the same volume.
Regarding uphauling, I don't think anyone mentioned that when you uphaul a board that sinks, your legs are submerged so you subtract the weight of that part of your legs from the equation.
As for wanting 20 litres more board volume than your weight, it depends on how good you are at uphauling, some people can easily uphaul boards equivalent to their weight. People have even told me that it gets easier to uphaul when the board sinks because the board becomes more stable, though I haven't noticed that personally. Of course it tends to become impractical if you take it too far - if there's not enough wind to waterstart then it's hard to sail a board that small at all.
