Size by height and board type
Your height sets the length, not the volume. At 5'9": a shortboard comes out at 5'11", a hybrid at 5'9", a fish at 5'7" and a mid-length at 7'5". The longboard is the exception, because its length is set by how it is ridden rather than by your body.
Length is the dimension people ask for most and the one that decides least. It does two things: it lets you fit on the board while paddling, and it matches the curve to the size of wave. What actually tunes flotation is width and thickness, and those come out of the volume you need.
| height | Softboard | Mid-length | Fish | Hybrid | Shortboard | Longboard | Gun |
|---|---|---|---|---|---|---|---|
| 5'1" | 8'1" | 6'9" | 5'4" | 5'6" | 5'6" | 9'0" | 7'0" |
| 5'3" | 8'3" | 6'11" | 5'4" | 5'6" | 5'6" | 9'0" | 7'0" |
| 5'5" | 8'5" | 7'1" | 5'4" | 5'6" | 5'7" | 9'0" | 7'1" |
| 5'7" | 8'6" | 7'3" | 5'5" | 5'7" | 5'9" | 9'0" | 7'3" |
| 5'9" | 8'6" | 7'5" | 5'7" | 5'9" | 5'11" | 9'0" | 7'5" |
| 5'11" | 8'6" | 7'7" | 5'9" | 5'11" | 6'1" | 9'0" | 7'7" |
| 6'1" | 8'6" | 7'9" | 5'11" | 6'1" | 6'3" | 9'0" | 7'9" |
| 6'3" | 8'6" | 7'10" | 6'1" | 6'3" | 6'5" | 9'0" | 7'11" |
| 6'5" | 8'6" | 8'0" | 6'3" | 6'5" | 6'7" | 9'0" | 8'1" |
The longboard row is flat at 9'0" because its length is set by how you surf it, not by your height. The softboard tops out at 8'6" above 6'1": past that, volume comes from width and thickness rather than length.
Ranges, widths and fill factor
Every board type lives inside a range, and stepping outside it stops being that board. A 6'8" fish is no longer a fish, it is something else that paddles strangely. That is why the calculator, when the volume you need does not fit the shape you asked for, first stretches the board within its own range and only then switches shape, instead of handing you impossible dimensions.
| Board | Length | Width | Thickness | Fill |
|---|---|---|---|---|
| Softboard | 7'0" – 8'6" | 24 % | 2¾" – 3¾" | 0.60 |
| Mid-length | 6'6" – 8'0" | 26 % | 2⅛" – 3⅜" | 0.59 |
| Fish | 5'4" – 6'8" | 30 % | 2⅛" – 3" | 0.53 |
| Hybrid | 5'6" – 6'5" | 28 % | 2⅛" – 2⅞" | 0.57 |
| Shortboard | 5'6" – 7'0" | 27 % | 1¾" – 2⅞" | 0.55 |
| Longboard | 8'6" – 10'0" | 21 % | 2½" – 3½" | 0.61 |
| Gun | 7'0" – 9'6" | 22 % | 2⅜" – 3⅜" | 0.52 |
Width is expressed as a percentage of length. The fill factor is the fraction of the length × width × thickness box the board actually occupies: a fish fills 0.53 and a longboard 0.61, which is why two boards of the same length can float completely differently.
How volume becomes dimensions
Board volume is not length times width times thickness: that would be a brick. It is that box multiplied by a fill factor that captures how close the real shape gets to it, running from 0.52 on a finely foiled gun to 0.61 on a longboard. With the target volume and each shape's fill factor you solve for width and thickness, and that is what you see in the calculator result.