How Should Swim Fins Fit? How to Get the Right One

Sometimes when I’m swimming, I’ll notice a lone fin floating along the water’s surface, and a swimmer frantically looking for it. This swimmer probably felt that the fins fit him snug, only for it to slip off mid-kick. I’ve made this mistake myself before. What gives?

When buying or renting a pair of fins, you cannot rely entirely on your shoe size for determining a good fit. Instead, find a pair that fits snug on your feet; better for it to feel a bit too tight than loose. When you enter the water, your feet will shrink in size slightly so that the fit ends up being perfect. How snug is that? If you can squeeze in only two fingers into the foot pocket, that’s a good fit.

Fins that fit too tight are ones where you cannot even squeeze in a single finger in the foot pocket. Conversely, if you can squeeze in multiple fingers, then the fit is too loose. If your toes feel cramped for space, then the fins are simply too small. These are some quick and easy guidelines you can follow to get a good fit 90% of the time.

If you want to learn how you can get swim fins that perfectly fit 100% of the time, then keep reading on and I will reveal all the details below.

Buying from a physical store vs. online

With how much of a juggernaut Amazon has become, and other retailers shifting towards having online stores, many people are now buying their fins online instead of in-person at a store.

There are some downsides to buying clothing online, which is that you aren’t 100% sure if they will fit you and you also cannot be sure if they are even comfortable. Any store worth their salt will offer a solid refund policy, but sometimes you’re SOL.

If you’re buying fins from a dedicated dive shop, then you can ask the staff (likely experienced swimmers or divers) for advice on how to get one that fits you snug.

Most importantly, you can try on the fins yourself and feel how comfortable or uncomfortable it is. You can even compare the length and width of the swim fins to your shoes to immediately get a sense of roughly what size and length a pair of fins needs to be for your feet.

I have nothing against buying fins or any other kind of swimming gear online. It can be really convenient if you already know what you want. However, I must warn you that shipping ill-fitting fins back and forth is time-consuming and a hassle, so my tips will focus on trying on fins in-store.

If you want to buy your fins online, I highly recommend first going through the shopping experience in person. That way, once you find a pair of fins that you like, you can just order it online from that point on.

How to size your fins properly

Start with shoe size

If your shoes already fit your feet snug, then that is a good reference point to start with. Don’t just rely on the shoe size number; literally compare the sole of your shoes to the sole of a pair of swimming fins.

Don’t just compare the length, but also how narrow or wide the fins are compared to your shoes. Unfortunately, if you have wide feet like me, you may have to try multiple fins before you find one wide enough for your feet.

While the physical comparison is really nice to see, if you’re shopping online you will have to rely on your shoe size number (e.g. size 10 in shoes, try a size 10 swimming fin).

This doesn’t factor in the width of the swim fin, and there may be discrepancies between how sizes are measured, so this is not the most reliable metric.

Make sure it fits snug

Here’s a quick and dirty guideline that I find works well 90% of the time. You can test how snug it fits by sticking your fingers into the foot pocket. If you can barely squeeze in two fingers, that’s a good fit. Any more than that, it’s too loose; any less, it’s too tight.

If you are inbetween sizes, this can be a bit tricky. Your feet can actually shrink a little bit in the water, so a pair of fins that seems very snug might actually be a good fit when wet. Thankfully, you have some leeway because you can always wear fin socks if a pair of fins is a little loose on you.

Trying on the fins – dry vs. wet

When trying on the fins, if you plan on wearing fin socks while swimming, then you should try the fins with socks on. If you plan on going barefoot, then wear the fins barefoot as well.

It’s much harder to wear a pair of fins when it’s dry. So if you find yourself wriggingly and struggling to put them on, it’s fine as long as they are comfortable and snug once they are fully on. When it is actually time to use them at the pool, I recommend wearing them in the water to make things easier.

What you need to worry about is if a pair of fins can slip on easily when it’s dry, it’s going to slip off even faster when wet.

Furthermore, a loose fit can increase chafing and slipping around your ankle, both of which are annoying. With regards to chafing, your skin will become callous and it suddenly isn’t an issue anymore.

Conversely, if the chafing is so bad that you have an open wound, then you need to stop wearing the fins ASAP and let it heal. Consider wearing fin socks to protect your skin in the future.

Between sizes? Chafing? Cold feet? Wear a fin sock

Fin socks add an extra layer around your feet which can protect your skin from rubbing against the foot pocket. It can also add some extra padding (1-2mm) so that your feet can stop sliding around, and reduce the chances of fins slipping off.

Some people have poor circulation or just don’t like the feeling of getting cold feet, and fin socks can provide some extra insulation. Even in warm waters, you will be surprised at how quickly you can get cold so any bit of warmth is appreciated.

In the same way that I don’t wear shoes without socks, I personally like to wear fin socks just because of how comfortable they make wearing fins feel. If you’re bony like me, it can also add some extra padding around your bony bits.

If you have wide feet, be careful because fin socks will add some extra volume to your already wide feet. Unless you can find a pair of extremely wide fins that can accommodate that, then you might want to stay away from fin socks.

The bottom line

To summarize this article, swim fins should fit snug. I recommend shopping for fins in-person rather than online because it’s much easier to compare it sole to sole with your shoes, and you can try them on.

A snug fit means that you can still shove two fingers in your foot pocket. The fins should not restrict your blood flow or crush your toes; these are indicators that it’s too tight and small. If you can’t squeeze in two fingers, it’s too small.

I like to wear fin socks with my swim fins for the extra comfort, insulation, and chafing protection it provides. This also means that my swim fins need to be slightly bigger to account for the extra volume. Fin socks can help you add some extra volume to your feet if you’re inbetween sizes or accidentally bought a pair of fins that are slightly too large.

How your fins fit on land vs. in the water is slightly different. Your feet can actually slightly shrink in the water, so it’s better for the fins to fit snug on land. Also, it’s harder to put on fins on land, but don’t let that trick you into thinking a pair of fins is bad. If it’s comfy after you put it on, then that’s still a good fit.

You should now have a good idea of how swim fins should fit, so go forth and find yourself a comfortable, snug pair that fits like a dream.