What Is Boot Sole Length (BSL)? How to Find Yours Before You Buy Skis
We answer this question 10 to 15 times a day in the wintertime. Someone orders skis, we ask for their BSL, and there's a pause. It's the one number that stands between a new pair of skis and a mounted, ready-to-ride setup; and almost nobody knows it off the top of their head.
So here's everything you need to know about boot sole length: what it is, where it's hiding on your boot, and what to do if you can't find it.
What is boot sole length (BSL)?
BSL stands for boot sole length. It's the length of your ski boot's sole, measured in millimeters from the very tip of the toe to the very back of the heel, the two points that actually sit in your bindings.
It is not your shoe size. It is not your mondo size. It's a physical measurement of the plastic shell, and it's the number a shop needs to mount your skis when your boots aren't sitting on the bench in front of us.
The three numbers on every ski boot
There are three numbers associated with a ski boot, and people mix them up constantly. Here's what each one does:
| Number | Looks like | What it tells you |
|---|---|---|
| Mondo size | 24.5, 25.5, 27.0 | Roughly equates to your shoe size — the length of your foot. |
| Last | 98, 100, 102 | The width of the boot. A 98 is narrow, a 102 is roomy. |
| BSL | A three-digit number, in mm | The magic number. This is what we mount your skis to. |
Mondo and last matter when you're buying boots. BSL matters when you're buying skis.
Where to find your BSL
The number is stamped into the plastic of the boot, and it lives in one of three places:
- The inside of the heel
- The outside of the heel
- The bottom of the boot
Because it's molded into the plastic rather than printed, it can be genuinely hard to spot. Especially on a dark shell, or one that's seen a few seasons of walking across parking lots. Take the boot into good light, run your thumb over the heel area, and look for a three-digit number. We guarantee you it's there.
What if you can't find it or don't have the boot handy?
Happens all the time. Boots are at the condo, boots are in storage, the stamp has worn down to nothing.
In that case, get us the year, make, model, and size of your boot and look it up on our BSL size charts. We keep them organized by brand so you can find your boot and read the corresponding sole length straight off the chart.
Still stuck? Call us at 970-688-5485 or text 970-390-6224 and we'll walk you through it. This is genuinely a daily conversation for us, you're not bothering anyone.
Why BSL matters for your bindings
A ski binding isn't a fixed object. The toe piece and heel piece have to sit a specific distance apart, matched to the exact length of your boot sole, so the boot seats properly in both and releases the way it's designed to.
Get that distance wrong and you're not just uncomfortable, you're outside the release specification the binding was certified to. That's why we won't guess at it, and why we ask every single ski customer for the number before anything goes on the drill press.
Does BSL change if you switch boots?
Yes... and this is the part that catches people out. Two boots in the same mondo size from different brands can carry different sole lengths, because shell design, sole thickness, and toe and heel profiles vary between manufacturers. Even the same brand can change a model's BSL between model years.
So if you've bought new boots and you're planning to use last season's skis, don't assume you're fine. Check the new BSL against the old one:
- A small difference can often be handled by adjusting the heel piece, since most alpine bindings have a built-in adjustment range.
- A larger difference may push you past that range, which means a remount.
A shop can tell you which one you're looking at in about thirty seconds. Ask before you assume.
One thing mounting doesn't cover
We'll mount your skis to your BSL, it's free when you buy skis and bindings together, or $40 as a standalone service. But mounting is only half the job.
You still have to take your skis to a certified ski technician to set:
- Toe height — so the boot sits at the correct elevation in the toe piece
- Forward pressure — so the heel piece applies the right clamping force
- DIN setting — your release value, calculated from your height, weight, age, ability, and BSL
Those three adjustments are what make a binding actually release in a crash, and they require a technician with the right tools and certification. Skis we ship are mounted, not set. Please don't skip that step.
Quick answers
Is BSL the same as my shoe size?
No. Shoe size lines up roughly with mondo size. BSL is a separate millimeter measurement of the boot's outer shell.
Where is BSL written on a ski boot?
Stamped into the plastic on the inside of the heel, the outside of the heel, or the bottom of the boot.
Can you mount my skis without my boots?
Yes... that's exactly what BSL is for. Give us the number and we can mount to it without ever seeing the boot.
What if my two boots show different numbers?
They shouldn't. If they do, you're likely reading a different stamp (a mold number or shell size) on one of them. Send us a photo and we'll sort it out.
Do touring and GripWalk boots have a BSL?
Yes, same measurement, same locations. The sole type is a separate question. It determines which bindings your boot is compatible with, which we get into elsewhere in the series.
Full video transcript — Skiformation Series #1 | Boot Sole Length (BSL)
Chris here from Ski Town All-Stars in Vail, Colorado. Here at the shop, we get asked a lot of questions, and the answers aren't always easy to come by, especially for the average skier. So we decided to start a series. We're taking everything we know, all the vital information we've picked up over the years in the ski industry, and putting it together in one place. Ski information... Skiformation. See what we did there?
The Skiformation series is your one-stop source for ski questions, so you can buy your next piece of gear online with confidence.
This is how you find your BSL. BSL stands for boot sole length, and this is a question we have to answer about 10 to 15 times a day in the wintertime when we're selling a lot of skis. We need your BSL to be able to mount your skis to your boot when your boot's not here.
There are three numbers associated with a ski boot. The first one is the mondo size. That's going to be something like a 24.5 or 25.5, and it equates basically to your shoe size. The second number is the last of the boot, typically 98, 100, or 102 — that's the width of your boot. And the third magic number, the one we need to mount your skis, is the BSL.
That number is typically located in three different places on the boot: the inside of the heel, the outside of the heel, or the bottom of the boot. It's usually stamped into the plastic, so sometimes it's hard to find, but I guarantee you it's there.
If you don't have your boot handy, or you can't find the number on your boot, you can always use the year, make, model, and size of your boot and look it up on our handy BSL chart on our website.
And remember: we're going to mount your skis to your BSL, but you'll still have to take your skis to a certified technician to adjust toe height, forward pressure, and your DIN.
Thanks for tuning in to our new Skiformation series. We've got a lot more stuff in the works for you guys, and be sure to check out our channel for all your ski-related needs. And like always, be sure to like and subscribe.
The Skiformation Series
We get asked a lot of questions at the shop, and the answers aren't always easy to come by for the average skier. So we're taking everything we've picked up over the years in the ski industry and putting it in one place. Ski information. Skiformation. See what we did there?
Up next in the series: brake widths, what they do, why one size doesn't fit every ski, and how to match them to your waist width.
Ready to build a setup? Browse the ski shop, check out our Dream Setups, or call a pro at 970-688-5485, Monday through Friday.
