Surfboard Fin Size Calculator, and How to Order FinSciences Fin Sets

FinSciences Surfboard Fin Designs and SUP Fin Designs are Smaller Than Others.

It’s all about the AREA.  Less is more.  Less area ⇒ more speed and maneuverability.

Less Fin = More Fun!

Most companies talk about depth/height of their fins, but say little to nothing about the overall area of a whole set of fins together. But TOTAL FIN AREA is a BIG factor in how fins handle.  So knowing your fin-set’s total AREA is key.

You can use our rules of thumb to order a set, or you can calculate the AREA of FinSciences fins you need, IF you know the area of your current set.

Learn more about surfboard fin deisgn and SUP fin design by following the links at the bottom of this page, and on out Surfboard Fin Science Page.

What Do You Ride? Here are some rules of thumb. Check out our surfboard fin size calculator for more.

Twin Fin

  • Twin fins tend to be about 40 in.² for a set of two.
  • Get two 5.7″ fins and decrease your area by about 25 percent for more speed.
  • For lighter surfers, downsize to two 4.7 in.² fins, but that’s pushing it.

Thruster Set

  • Thruster sets are usually about 45 square inches per set.
  • Get a set of three FinSciences 4.8″ fins for a looser ride.
  • Or get two 4.8″ fins plus a 5.7″ tail fin for a bit more hold.

Quad Set

  • Quad sets are usually about 60 square inches per set.
  • Get four 4.8″ fins for a looser ride and lots of speed.
  • Or for more hold, get two 4.8″ fins plus two 5.7s.


  • Longboard fins tend to be large, often 45 in.² or more.
  • Get our 9¼” 30.7 in² WG2 fin.—this works well if if you currently have a 2 + 1 setup. Pop out the sidebites and go single fin with the WG2—you’ll be surprised at the performance increase made possible by decreasing your total area so dramatically.
  • If you really need sites for extra bit, add in two 4.8″ fins or two 5.7 ” fins.
  • Rule of thumb: bigger riders, flatter rocker, softer rails (like classic longboards) need more fin to turn. But our WG2 works excellently as a single fin in  classic longboards.


  • Paddleboard fins tend to be large, 50 and even 60 square inches.
  • Get our 9¼” WG2.
  • If you have a really big board, or extra-powerful strokes, add in a couple sidebites, starting small with two 4.8″ fins as sidebites, going to two 5.7″ fins if you really need the bite.

This Surfboard Fin Size Calculator Helps Pick Fins 20 to 30 Percent Smaller. Less Fin = More Fun!

1. What’s your CURRENT fin-set size (TOTAL area, all fins combined)?

2. Know your fin-set-total-area range? Choose FinSciences Fin Sets From This Table.

  • Single fins shown in green,
  • Twin-fin sets shown in tan,
  • Thruster sets shown in orange,
  • Quad sets shown in yellow.
  • 2 + 1 sets shown in blue.
Surfboard Fin Size Calculator 1

3. Shop.

Go to our shop page, and order the fins you’d like.

Surfboard Fin Size Calculator 2

Examples—Using Our Surfboard Fin Size Calculator

> Single-fin-fin-sizing example:

Enter “42″ in the calculator (the size of many typical longboard fins).

The calculator yields a range of 29.40 and a high of 33.60 sq. inches.

Then check the fin combinations table and you can see that you could get a WG2, or two SB larges, or three SM smalls—and all would be within the range. You might be able to go even smaller by using fewer fins in a multiple-fin set. Opt for fewer fins given a choice.

> 2 + 1 fin-sizing example:

Enter “69,” in the calculator (the area of many 2 plus one setups (probably 40 sq. inches in the center fin, and about 14.5 sq. inches in each of the two sidebites)).

The calcuator yields a range of 48.3 to 55.2 sq. inches.

Then check the table. You could go with a 2 + 1 setup of a WG2 and 2 SB smalls. And you might be able to go even smaller. I’m about 185 pounds, 5’11″, and generally ride a 9’6″ performance longboard. I popped out the sidebites and ride it as a single fin, shedding about 50 percent of my total fin area—and it works great! Many have done the same thing and have reported excellent results. Part of the reason for this is speed from shedding the toed-in fins.  Depending on the board-bottom shape, toe-in can create a lot of drag by virtue of the inward angle of attack.

> Thruster-fin-sizing example:

Enter 43.8 in the calculator. Thruster medium sets often have three fins, each of which is about 14.6 sq. inches, times three = 43.8 total square inches.

The calculator yields a 20 – 30 percent reduction range of 30.66 – 35.04 sq. inches.

Check the table. Try three smalls. If you feel that it’s too loose, or you’re spinning out, or your bigger and need more oompf, add a bit of area, try 2 smalls and a large, or 2 larges and 1 small.

> Quad-fin-sizing-example:

Enter 54 in thee calculator.

Quad sets often have a couple big fins up front, like 15.5 fronts with 11.5 rears, a total of 54 sq. inches. The calculator yields a range of 37.80 – 43.20 square inches, a reduction of 20 to 30 percent.

So check the table and try 4 smalls, or 2 larges and 2 smalls.

Downsizing your total fin area decreases drag. Check out these videos about drag.

Don’t Miss Great Waves!

50-second video

The Size Compromise

72-second video.

Drag Explained in 60 Seconds

60-second video.

Other Resources About Drag, Lift, and Reynolds Numbers

These factors all go into surfboard fin design and SUP fin design. The resources below are general, beginning-level discussions, but still do an excellent job explaining drag, lift, and Reynolds numbers, albeit in contect of airplanes, not surfboard or SUP fins.

But both air and water are fluids and behave in much the same way, although the the fluids have different densities, and although fins and wings are operating at different Reynolds number ranges.