How To Choose Ski Boots (For Perfect Fit and Flex)

Buying a new ski boot can be a daunting task. It’s one of the most important bits of gear you need to have in order to go skiing, and it can have a massive influence on both your comfort levels and how well you can ski. So, choosing the right ski boots for you is essential.

To choose the right ski boots for the right fit and flex, you must accurately measure the dimensions of your feet and then choose your level of flex according to your size and skill level. It’s usually best to use heat molding to get the perfect fit.

Sometimes a ski boot that feels comfortable in the ski shop can be misleading to how it will feel on the slopes or in deep powder. Many factors go into choosing the right ski boot for the type of skiing you plan to do, and below we’ll go into more detail about each one.

Ski Boot Fit And Flex

Fit and Flex are the two most important factors to consider when buying a new ski boot. To find the perfect fit, you must first accurately measure your feet. If you have the money to spend, we recommend getting a custom boot liner and footbed with the help of a heat mold.

A tight-fitting boot that doesn’t account for the height of your foot’s arch, or the width of your toes, is only going to cause pain in the long run. It is possible to find a retail boot that fits without heat molding, but most skiers will agree, the heat mold is worth the money. Having a boot that perfectly fits your foot increases your performance and decreases your risk of injury.

Flex Number

You then need to find your flex number. A ski boot flex number refers to how much pressure it takes to bend your boot. This number is crucial as it has a significant impact on how quickly your skis respond to you. Flex number depends mostly on your size and skill level. The heavier and more skilled you are, the higher the flex number (and so the stiffer) your boot should be.

A numerical rating system is used to rank ski boot flex, with 60 being on the low side and 170 being on the high side. It is also essential to reflect on the type of skier you are. The ski boots you need for the bunny slopes versus the ski boots you need for steep backcountry will vary greatly. Take some time to assess your needs and what kind of terrain you plan to use your boots on.

How Ski Boots Should Feel

If you are new to skiing, the feel of a ski boot can be overwhelming and uncomfortable. It is important to know how ski boots should feel in order to purchase the correct size. Ski boots are unique in that they must be tight fitting to control the skis they are attached to.

A common mistake many beginners make is upsizing their boots when they feel tight while trying them on. They don’t realize that ski boots pack out with a small amount of body heat and after only a short time skiing. Skiing with boots that are too big can be hazardous and lead to injury. A tight fit is of the utmost importance.

In the ski shop, your toes should be lightly touching the front of the boot because, when attached to your skis, your toes will naturally pull back away from the front. Your heel should be secure without any movement when buckled down and flexing forward. 

Measuring Your Feet With Heat Mold Technology

The best way to accurately measure the dimensions of your feet is with a heat mold. Some ski shops don’t have this technology, but if you’re an aggressive skier with a lot of skill, it is imperative to find one that does. Even if you are not an advanced skier but have high arches or extra wide feet, you may want to spend the extra cash for this technology.

It’s important to note that while the ski shop can always make more room in your ski boot with heat molds, you cannot take the room away once it’s made. It’s always better to err on the side of caution and go tighter. The last thing you want is to lose a snug fit after a couple of runs.

If You’re Lucky

If you are one of the lucky ones that tries on a new boot and it has a tight feel without being uncomfortable, you can skip the heat molding process of the liners and only heat mold the footbed. While skiing, the heat from your body will mold the liners to your feet. The heat molding process begins when the boot fitter takes out the footbeds of your liners and places those liners in an oven.

Foam caps are placed on your toes to allow for extra toe space. Once heated, the liners are placed back in the ski boot and the ski boot placed back on your feet. The next step is to stand on a raised block that shifts your weight forward for ten minutes to mimic the stance you will take while skiing.

After your liners take the shape of your feet, it’s time to heat mold the footbeds. Unlike the liners, you will be sitting down for this part of the heat molding. You want an unweighted foot because pressure causes changes in the shape of your foot and thus in the shape of the mold.

Next Steps

While skiing, you want your feet to stay in their normal resting position as much as possible to prevent circulation loss or freezing on a cold day. A base mold is taken by placing your feet on a squishy foam pillow while the footbeds are placed in a separate oven. Once heated, the footbeds fit into the base mold, and then your feet are placed on top of the footbeds.

The next step is to sit for another ten more minutes while they take on the form of your feet. Next, the boot fitter begins a meticulous trial and error of grinding the footbeds where needed and potentially adding heal stabilizers to secure the foot in the boot further. Now your feet have been accurately measured, and your chances of discomfort are minimized. 

Measuring Without Heat Mold Technology

If you choose to forgo heat molding, you want to make sure you measure your feet as accurately as possible. The best way to do this is to measure the length of your foot from your heel to the tip of your longest toe. For ski boots, this length is always measured in centimeters.

When calculating the width of your foot, always start with the knuckle of your big toe, or first metatarsal, to the knuckle of your pinky toe, or the fifth metatarsal. The width is always measured in millimeters. The width of the boot is also known as the boot last.

Choosing The Right Brand

While shopping for ski boots, something to keep in mind is that as the boot gets longer, it will always get wider, and as the boot gets shorter, it always gets narrower. We recommend trying on multiple brands to find which brand fits your feet as different brands will have different length to width ratios.

Another thing to keep in mind is to make sure you properly buckle your ski boot by starting with the correct buckle. Start with the buckle just above your ankle. This is usually the second buckle up from the top, then work your way up to get a snug fit around your calf and shin.

Finish by buckling the bottom buckles over your instep (top of your foot) and toes. Then, do the power strap last to secure everything firmly in place

Figuring Out Your Flex

Ski boot flex has a massive impact on how your skis respond, how your skis feel in deep powder, how your skis turn, and the point at which your skis eject from their bindings. The higher the flex rating, the stiffer the boot.

If you are the type of skier that sends it down steep chutes, you will want an extremely stiff boot. This is because the boot will be under a lot of force and need to remain unchanged to retain kinetic energy. If you are cruising around on groomers with the family, your boots will not be under such pressure, and the flex number can be much lower.

Finding The Right Flex Number

Usually, a beginner to intermediate male would want a flex number from 60-100, while an advanced male skier would want a flex number of 100-130. A beginner to intermediate female skier usually weighs less than her male counterpart and should have a flex number between 50-80, while a female shredder should have 80-110.

Flex numbers above 130 are reserved for exceptionally large and advanced skiers, but I find very few real-world situations where a flex number above 130 is practical. One exception to this would be ski racers, who typically have flex ratings above 130.

Something helpful to remember is that there is no standardized flex measurement across all brands. If you prefer a 110 flex number for one brand, it might not feel like a 110 for another brand. Flex also has a lot to do with the number of buckles as well as the design of the boots. 

Snow Conditions And Flex

If you’re an advanced skier, snow conditions come into play when figuring out your flex number. It’s helpful to look at the science of flex when discussing snow. With softer boots or lower flex numbers, more kinetic energy is lost in each turn. When making a turn, the ski pushes back against the ground sending resistance up into the ski boot.

That resistance then sends the skier’s body in the direction they want to go. With a soft flex, kinetic energy is lost in the boot’s flex, making what could be a snappy turn a fair bit slower. A stiffer boot has faster rebound and stability, making it an excellent choice for hardpack snow.

Rigid Boots

More rigid boots do well in hardpack snow, packed powder, ice, along with stiffer, longer skis because there is a greater force pushing the skier back. Skiing deep powder is where things start to get a little tricky. Anyone who regularly skis deep powder knows that snow like this forces the skier back significantly more.

There is a lot of debate around powder skiing, but many people prefer a softer flex number in the deep snow. This does not mean you should choose an extremely low flex number, but a softer flex number that is still on the higher side (no less than 80) is where you want to be.


If you are a big mogul skier, you don’t want a lot of pushback with impact. You want to lose as much kinetic energy as possible which each bump. This is why most mogul skiers also prefer a lower flex number. 

Boot Type And Flex

As we mentioned earlier, every ski boot manufacturer has their own flex rating system. But the flex rating also varies between boot types. For example, a racing ski boot might have a medium flex rating but feel more like a high flex rating in its recreational counterpart.

Another example of this would be someone who spends a lot of time in the park. If you go with a high flex rating, you will probably be dealing with a lot of shin bang on your landings. In this instance, a lower flex rating will be more comfortable.

Three-Piece vs Two-Piece

There are also three-piece boots and two-piece boots. Three-piece boots are the older style with a removable tongue, a shaft, and a base. The tongue controls the flex on these boots allowing for pressure to bend the boot more easily. This is because the removable tongue is made with less material and, therefore, more easily forced forward under pressure.

With a two-piece boot, the only pieces are the foot and the shaft. The foot piece physically stops the shaft piece from leaning too far forward, resulting in a much stiffer boot.

The liners also play a large part in the flex of these boots. The three-piece boot liner folds down in the front with the tongue piece. The two-piece boot has a wrap-around liner that comes apart at the sides. This means there are two layers of liner on your shin, preventing your ankle and shin from flexing forward

Alpine Touring Boots And Flex

If you are the type of skier that hates lift lines and has no problem earning your turns, then an alpine touring boot might be the perfect boot for you. Touring boots must have the best of both worlds. They must be light and comfortable for the hike up and stiff and durable for the ski down.

Where you find the balance between these two conflicting ideals depends on what type of skier you are. If you prefer long tours across rolling hills, a lower flex rating is probably suitable for you. If hiking to find the perfect line is your thing, you probably want a pretty stiff boot with a flex rating above 110.

Hybrid Boots

One type of alpine touring boot that is growing in popularity is the hybrid. This boot can function like an alpine skiing boot at the ski resort and an alpine touring boot in the backcountry.

These are great if you don’t have the funds to have a resort setup and a separate backcountry setup. If you decide to buy a hybrid boot, make sure it fits into your resort binding. Some of these hybrids only fit into one or two specific resort bindings. There are versatile hybrids out there, so just make sure you choose the correct one for your specific situation.

One of the major and most important differences between an alpine skiing boot and an alpine touring boot is the tech fitting in the toe. This refers to the tiny holes and screws that attach the boot to the alpine touring binding. These bindings are similar to that of a telemark binding, where the heel of your foot is free to allow you to walk up the hill.

Alpine Skiing Boots

Alpine skiing boots (resort boots) don’t have this tech fitting, so if you plan to attach your boot to an alpine touring binding, then these boots are the right boot for you. Lightness is of some importance to an alpine tourist, but most would rather have the stiffness and performance for the ride down, even if it means a little extra weight for the hike up.

Another thing to consider if you plan to spend a lot of time in the backcountry is walk mode. Walk mode is usually a toggle found near the back of your ankle that releases the upper shaft of your boot from the bottom allowing for more motion.

Benefits Of Walk Mode

Some argue that this affects the rigidity of the boot, but most alpine tourists are glad to have the feature, especially during creek crossings or long ascents. Some people like to have walk mode on their resort boots to make long treks from distant parking lots more comfortable.

Final Thoughts

Ski boots are an extremely technical aspect of the sport. Accurately measuring your feet is of the utmost importance. Whether you are measuring the old fashion way or with the cutting-edge technology available to you, getting the right size and flex for your ski boots will make your skiing much more comfortable, and will allow you to perform at your best.

Only by knowing the type of skiing you wish to do will you be able to determine your flex number. This can be done by considering your size, your ability, your style, the places where you will likely be skiing and the typical snow conditions of those places. Knowing yourself as a skier will help you make the right choice and eliminate buyer’s remorse!