You buckle in on the first run of the day. Within twenty minutes there’s a hard band of pressure across the top of your foot, right where your laces would sit on a running shoe. Your toes go numb.
You crack the buckles open a notch, then two, then all the way, and the pressure barely moves. By lunch you’re in the lodge with your boots off, wondering whether you bought the wrong size.
You probably didn’t buy the wrong size. You bought the wrong volume.
Length was fine. Width was probably fine too. The problem is the vertical space inside the shell, the distance from the footbed up to the underside of the boot’s tongue. Skiers call that the instep, and it’s the fit dimension almost nobody shops for.
If you’ve seen “Volume: High” on a boot card and skipped past it, this is what that line is telling you.
What is ski boot volume?
Boot manufacturers build the same model in different internal volumes and label them LV, MV, and HV.
- LV is low volume
- MV is mid or medium volume
- HV is high volume
You’ll see the letters right in the product name. Tecnica Mach1 MV. Fischer RC4 Pro MV. Lange Shadow MV.
Some brands put the tier in the line name instead of the product name, which is why a Nordica Speedmachine and a Nordica Sportmachine are different animals even at the same flex and the same size.
The tier covers more than width. When a brand drops from HV to MV to LV, it takes volume out of the whole shell, and a good chunk of that comes out of the height over your instep. Two boots can share a 100mm last width and still feel completely different across the top of your foot.
That’s the part that catches people. You can shop width, because width is a number printed on the spec sheet. Almost nobody publishes an instep measurement, so the volume letter is the only signal you get.
Why can’t a bootfitter just fix it?
Take a boot that’s too narrow to a good fitter and they have real options. They can punch the shell, heating a spot and pushing it outward. They can grind material off the inside. They can stretch it.
You’ll get four to six millimeters of width, it holds permanently, and it typically runs $50 to $150.
Take a boot that’s too tight over the instep to that same fitter and the toolkit nearly empties.
The shell can be pushed out sideways. It cannot be made taller. There’s no punch that raises the roof over your foot, because the roof is the structural spine of the boot and the place the buckles anchor.
What a fitter can do is take height out from underneath you. A thinner bootboard, a lower-profile footbed, thinning the tongue of the liner. Stack those together and you might gain two to four millimeters in height inside the shell, and you may pay for some of it in arch support you wanted.
That asymmetry is the whole reason volume deserves your attention up front. Too narrow is a service appointment. Too wide is a foam shim or two, cheap and reversible. Too tight over the instep is a boot you stop skiing.
The good news runs the other direction. A boot with more instep room than you need is one of the easiest problems in bootfitting. Pad the tongue, add a thicker footbed, size the liner up. Excess volume is a comfort issue with a fix that costs almost nothing and can be undone the moment you change your mind.
How much do insteps vary?
We’ve measured this across our own scans, and the spread is bigger than most skiers assume.
Across 300+ Wayfinder foot scans, the median instep height is about 63mm. The lowest tenth of feet sit near 58mm and the highest tenth near 69mm. That’s an 11mm range between a low-instep foot and a high-instep foot.
For a sense of scale, mondo sizing counts foot length in millimetres, so a full boot size is 10mm. That 11mm spread is a whole size and then some. It’s a difference you’d never tolerate quietly in any other dimension, and it’s sitting in a measurement most skiers have never had taken.
This isn’t unique to our skiers. Volumental, the company whose scanning technology we use, published an analysis of 1.2 million foot scans across North America, Europe and Asia in Scientific Reports. Instep height does climb with foot length, but not evenly. For North American feet it gains about 0.29mm per millimeter of foot length up to a 255mm foot, then flattens to 0.09mm above that. The bigger your feet, the less your shoe size tells you about your instep. The same data shows European men measuring significantly taller over the instep than North American men in every length class the study looked at, with a more mixed picture for women. Same shoe size, different foot.
The more useful finding is how loosely instep relates to everything else you already know about your foot.
In our data, foot length predicts instep height about as poorly as it predicts width. Both correlations land near 0.71, which sounds high until you translate it: length explains roughly half the variation and leaves the other half unaccounted for. Knowing your shoe size tells you something about your instep, and it leaves plenty of room to be wrong.
Two skiers who wear the same mondo size, with the same width, can need different volume boots.
See your instep measured, free
Interpreting your own numbers
If you’ve scanned with us, your results page shows a Volume line on each recommended boot. Here’s how to read it against yourself.
Your instep sits well above average for your foot length. You want MV or HV. An LV shell in your size will likely give you that band of pressure across the top, and no fitter is going to relieve it. Start roomier and take the fit in with a footbed if it’s loose.
Your instep sits near the middle. Most MV boots will work. You have the widest selection of anyone, and you can shop on flex, last width and price without volume narrowing the field much.
Your instep sits well below average. LV and MV both work, and an LV shell will hold your foot down better. In a high-volume boot you’ll likely get heel lift, because there’s more room above your foot than your foot fills, and buckling harder to chase it crushes the sides.
One caveat worth stating plainly. Your instep height and a boot’s internal height are two different measurements taken two different ways. We’re comparing you against the manufacturer’s own volume tier, not against a published number for the space inside that shell, because no brand publishes one. The tier is the best signal available and it’s a good one, and it isn’t a caliper.
How do you know if you have a high instep without a scan?
You don’t need equipment to get a first read.
Look at your shoe laces. If the tongue of your everyday shoes sits high and the laces pull the eyelets close together, you probably have a low instep. If your laces run out of adjustment before the shoe feels snug, and the eyelet rows stay far apart, your instep is on the high side.
Think about your dress shoes. Loafers and slip-ons are unforgiving over the instep. If they always feel tight across the top even when the length is right, that’s a signal.
Remember your last boot fitting. Skiers with high insteps tend to collect a specific complaint. The boot feels fine in the shop, then the top of the foot goes numb after twenty minutes of skiing. Loosening the buckles doesn’t fix it, because the pressure isn’t coming from the buckles. It’s the shell closing down on the foot from above.
Try the shell check. Pull the liner out, put your bare foot in the empty shell, and slide your toes to the front. You’re normally checking for 10 to 15mm behind your heel. While you’re in there, notice whether the shell touches the top of your foot before you’ve even buckled anything. If it does, that shell is too low for you regardless of what the length says.
That last one is the closest you’ll get to a real measurement without a scan, and it’s worth doing before you buy any boot you plan to keep for five seasons.
What should you do with this?
Shop the volume tier before you shop the model. If you know you’re high volume, filtering to MV and HV first saves you from falling for a boot you’ll never be comfortable in. The letters are right in the product name for most brands.
Treat a snug instep in the shop as disqualifying. Boot shells pack out around your foot’s width over the first few days. They do not gain height. A boot that presses on the top of your foot in a carpeted shop, standing still, at room temperature, is going to press harder on a cold morning with your weight on it.
Treat a roomy instep as fixable. If everything else about a boot is right and it feels a touch loose over the top, buy it and shim it. A tongue pad costs a few dollars and takes a minute.
Get the actual measurement if you can. Instep is the fit dimension you’re least likely to have ever had measured, and the one you can do least about after the fact.
Our scan measures your instep height along with length and width, and every boot we recommend gets checked against it. When a shell runs snug over the top for your foot, it drops down the list. When there’s room to spare, it doesn’t get penalized, because that’s the direction a fitter can help you with.
Two photos with your phone, about two minutes, no appointment, and no drive to Truckee.
Scan your feet and see your matches
Related reading
- Last width, explained
- Ski boots for wide feet
- Ski boot mondo sizing guide
- How tight should ski boots be?
- What is ski boot flex and why it actually matters
Source
Jurca A, Žabkar J, Džeroski S. Analysis of 1.2 million foot scans from North America, Europe and Asia. Scientific Reports 9, 19155 (2019).
doi:10.1038/s41598-019-55432-z. Read the paper
Published open access under a Creative Commons Attribution 4.0 International licence. Lead author Ales Jurca is affiliated with Volumental AB, whose scanners collected the data across 712 retail stores between November 2017 and August 2018.
