What size fin do I need for my longboard?
This is the most common question we get. And the answer depends on what kind of longboard you ride and how you want it to feel.
The short answer
If you are not sure, start with a 9 inch fin. That is the sweet spot for most longboards. It gives you enough hold to nose ride and enough pivot to turn.
Fin size by board length
9 foot logs and bigger. Go 9.5 to 10.5 inches. You need the extra fin area to hold the tail in trim and keep the board tracking through noserides. A fin that is too small on a big board feels skaty and unstable.
8 to 9 foot boards. 8.5 to 9.5 inches. This is the everyday range. Most single fin mid-lengths and standard longboards sit here. At 8.5 you get a looser feel. At 9.5 you get more lock-in for noseriding.
7 to 8 foot mid-lengths. 7 to 8.5 inches. Smaller fins let a mid-length pivot and turn like a much shorter board. If you want to surf it like a big shortboard, go smaller. If you want to cruise and trim, go bigger.
What happens when you change size
Drop from a 10 inch fin to an 8.5 on the same board and it feels completely different. The tail frees up. Turns get tighter. The board feels lighter. Go the other way and everything locks in. More hold. More drive. More stability through flat sections.
There is no wrong answer. Just different feels.
A note on fin position
Your US Box lets you slide the fin forward and backward. Move it forward and the board loosens up. Move it back and it locks in. Before you buy a new fin, try moving your current one. It might be all you need.
Still not sure
Pick the fin that matches your board length and decide which feel you want. Loose and pivoty? Go smaller. Locked in for noseriding? Go bigger. If you are between sizes, start with the bigger one. You can always slide it forward to loosen up.