Beginner. Intermediate. Expert. It's over. You choose your ski boot flex by physics.

Q: I'm renting first. Does it matter?

Yes. The first days decide if you keep skiing. Ski your first runs in the rental boots with FlexFinder in your pocket, enter the flex printed on the boot, and you'll see if it's too low. Then ask the rental counter for your number.

Questions about your flex?

Start with the question you have.

Short answers in plain words. The longer read is in Articles.

1I'm buying boots. What should I buy?
2I'm renting first. Does it matter?
3Is it really my boots?
4What's going on in the boot?
5Why not choose by level?
6How can a phone measure this?
7What does my number mean?
8Isn't a lower flex more comfortable?

1 · I'm buying boots. What should I buy?

Three choices: the flex for your skiing, the fit for your foot shape, the forward lean for your position.

Get your flex number first. Pocket your phone, ski two to three runs, and FlexFinder calculates the flex index that supports you. It lists the boots closest to your number from 328 boots across 11 brands.

Then take the number to a bootfitter. They handle the fit: length, width and shape. Walk in saying: "I'm looking for a 120 flex boot." You bring the flex index.

Ask about forward lean too: how far forward the boot holds your shin. A more upright boot is easier to start in. More forward lean is more aggressive. This is where your level does play a part, because trusting the boot with your weight takes time.

What your number means › In the shop ›

2 · I'm renting first. Does it matter?

Yes. The first days decide if you keep skiing.

Most people rent before they buy, to see if they like it. That is where most beginners are lost: in the US, about 4 in 5 never become regular skiers. We think that's a disaster for the sport.

Many reasons play a part. We believe the boot is one that gets overlooked: a boot that doesn't support you hurts, throws you off balance and makes you afraid of falling.

Ski your first runs in the rental boots with FlexFinder in your pocket, enter the flex printed on the boot, and you'll see if it's too low. Then ask the rental counter for your number.

Is it really my boots? ›

3 · Is it really my boots?

Me: “Let’s turn.”
My skis: “Let’s not.”
My boots: “Told you so.”

Fix your boots, and your skis will follow.

If skiing felt harder than it should, some of this may sound familiar.

What skiers tell me, every week

It's difficult to learn.
You struggle to relax, to stay in balance.
The boot gives you no support.
You curl up your toes to try to keep your balance.
No support forward or backward.
The ski lives its own life.

Intermediates tell me something else: they stop getting better, and difficult terrain, hard snow or deep snow gets scary.

“Most people blame themselves. In my experience, it's often the boot that doesn't support them.”

BBBernt Blankholm, ski racer, coach for over 40 years, boot and ski developer. What he sees at his bench, not a study.

Two to three runs
to check your boot

4 · What's going on in the boot?

The boot does not give you the right support. So you blame yourself.

“Nine out of ten beginners and intermediates I see are on the wrong flex index, most often too low, especially if they are tall or heavier.”

BBBernt Blankholm, ski racer, coach for over 40 years, boot and ski developer. His observation, not a study.

A boot with the right flex index keeps you in balance, front to back. When you bend your ankles forward, it turns that into pressure on the tip of the ski. The ski bends; the boot supports you while it does. When the boot doesn't support you in balance, your body tightens up. You try to hold yourself: with your thighs, your calves and your toes.

Often the flex indexNo support forward. Thighs burn, calves cramp.

Bootfitters report that when your boot flex is too low for you, it doesn't support you when you lean forward: your weight drifts back onto your heels, and your legs do the work. Too high is no better: you can't bend your ankles, so you can't get forward either.

Who can help: FlexFinder calculates your flex index.

Often the fitCurled, gripping toes. A heel that lifts.

Curled toes often mean the boot is too big. There is room to move, so your toes grab to hang on. The US ski-area trade magazine has called boot fit beginners' number-one stumbling block.

Who can help: your bootfitter.

Either way, the boot isn't holding you. It can be both, which is why we send you to a fitter with your number.

These are signs, not a diagnosis. Technique, tiredness, snow and skis play a part too, and what bootfitters report comes from practice, not from controlled studies.

Too low doesn't support you.
Too high holds you back.

About you: height, weight, ski radius, current boot flex 100

5 · Why not choose by level?

Your level depends on where you learned. Your physics doesn't.

In the shop you're asked your level. Most flex charts we reviewed start there. Your weight, if it appears, is usually a footnote, and none of the charts or boot finders we reviewed measure how you actually ski. FlexFinder does, from two to three runs: it records your skiing with your phone's sensors and works out what your boot has to handle.

Level is a poor guide. Nobody rates it the same way, not even you. In our experience, a beginner from Mexico and a beginner from Austria are not the same skier.

Your body is the same wherever you learned, and so is the physics of your skiing. That's why FlexFinder asks about your body and measures how you ski, instead of asking your level.

None of this is the shop's fault. The model is what's broken: flex has long been sold by ability level and by price. We think price shouldn't decide your flex.

Your body, not your level

Why your level misleads

ISO 11088The binding standard takes your skier type “as assessed by the skier”.

Norway · 512 skiers and snowboardersHow people rated themselves agreed only “low to fair” with a watched test run.

NetherlandsAbout 4 in 5 recreational skiers rated themselves higher than ski instructors did.

“Level 3”Still a wedge at one US ski school. Parallel turns at another in Canada.

6 · How can a phone measure this?

Phone in your pocket. Two to three runs.

Tell the app your height, your weight, your ski sidecut (the radius printed on the ski) and the flex index of your ski boots. Then go skiing. Any run you're happy on.

The app records your skiing with several of your phone's sensors, and a physics model calculates your number. It spots each run on its own, so there is nothing to press on the hill. After two to three runs, you have your number.

27,000

measurements in a two-minute run. Your phone's motion sensors read your skiing 25 times a second. Not a guess.

The calculation is calibrated against real-world skiing data from thousands of sessions.

Runs found on their own

7 · What does my number mean?

Identifies your flex index.

You get one number: your flex index. For example 110.

It isn't exact to the last point, and it doesn't need to be. The number on a boot isn't standardised either, so in the store you and your bootfitter try boots around your number. For a 110, that naturally means boots from about 105 to 115.

Then a verdict on the boot you own: too low, too high, or right. If yours is a 100 and your number is 110, the app tells you in plain words: 10 points too low for how you ski.

Too high is not the answer either. In the one controlled on-snow study we know of, beginners in high-flex boots learned worse. It was small, with 1980s boots, and flex was not matched to body weight. That is our point: the right flex index for your body.

One number,
not a guess at your level

8 · Isn't a lower flex more comfortable?

Walk in knowing your number.

Take your number to a bootfitter, or to the rental counter. They handle the fit: length, width, shape, your feet, and those curled toes. You bring the flex index. Your fitter is on your side.

MythA low flex index is comfortable.

FactComfort comes mainly from fit: the width and shape of the boot.

Bootfitters treat width and flex as two separate choices. Width and shape are for your foot. Flex is for your body and how you ski.

of 328 boots, from 10 of the 11 brands, have a flex index of 120 or more in a high-volume (HV) fit.From the FlexFinder boot list

Your matches come from 328 boots across 11 brands: a shortlist to try on with your bootfitter. We sell no boots, and there are no affiliate links.

Download on the App Store

We sell no boots. Ever.

Boot matches: your flex 110, boots from 11 brands

Using the app

How to get your number

Enter your height, weight, ski radius and the flex of your current boots.
Ski two to three runs with your phone in your pocket. Any run you're happy on. The app finds each run on its own.
Get your flex number, a verdict on your own boots (too low, too high or right) and your boot matches.

Sometimes the app asks for a third run. That's normal: it wants more skiing before it gives you a number.

The whole family on one phone: results are saved for up to six skiers.

FlexFinder is an iPhone app (iOS 17 or later), in English for now. You pay once in the App Store. The price depends on your country, for example USD 12.99, GBP 12.99, EUR 12.99 or NOK 129, and the App Store shows the price for yours.

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Stuck, or a question we haven't answered? Email support@snowhow.ski.