Stack Height: Tool, Shoe Lab Data & In-Depth Guide

Posted on 20 July, 2021 by Jovana Subic

We spent 50+ hours on creating a tool and doing the research for this guide. We’ve covered stack height in great detail and backed everything with our lab data. Our tool will tell you which stack height works for you by using your criteria and going through the biggest running shoe database in the world. 

Stack height is the amount of material between your feet and the ground. It is measured when your feet are not in the shoes as the midsole will compress due to a person’s weight, distorting the data. It’s given in millimeters and includes the height (thickness) of the insole, midsole and outsole. 

For beginners, it’s best to choose running shoes that are not too flat (low to the ground) and not too high. Look for stack height in the 20-30mm range. 

In running shoes, we focus on both heel stack height and forefoot stack height. Zero-drop running shoes are the only case where heel stack height = forefoot stack height. In all other cases, the heel is higher than the forefoot. 

Tool: Which stack height do you need

Use our tool to find out which stack height range might work for you. Based on your criteria, the tool will go over 2,000+ running shoes in our database and offer THE 3 best-rated picks.

[Our devs are working hard on making this tool! Available soon :)]

Stack height and its correlation to footstrike, ground feel, runner’s weight - it’s all explained in detail below. 

Stack height categories 

Based on the heel stack height, we group shoes into 4 categories: 

  1. Barefoot running shoes (the lowest stack height: 3-8mm)
  2. Minimalist running shoes (minimal stack height: 3-13mm)
  3. Regular running shoes (medium stack height: 9-29mm)
  4. Maximalist running shoes (maximal stack height: 30-50mm). 

Barefoot running shoes have the lowest stack height - they are closest to the ground. They are also insanely flexible - usually, you can roll them up. These shoes can’t be missed, no other shoes have such thin midsoles. In them, you feel the ground only. They ask for a serious adaptation period and it’s best to use them on the soft ground only in the beginning. 

Example shown below: Merrell Vapor Glove 4

Barefoot minimalist running shoe

There are 5 minimalist factors that make a shoe minimalist. In the case of the stack height, the minimal one means you get to feel the ground more than the shoe. It also means your body might adapt to the terrain because your legs will have to absorb the impact. These shoes offer a “natural feel” while running - they won’t weigh you down or bother you with extra junk in the trunk. Runners use these shoes when a) doing tempo work or b) looking for minimalist running experience. 

If considering these for the first time, keep in mind that they:

  1. might increase the risk for Achilles tendon injury as this study has shown. 
  2. Might help with knee pain (as explained here). 
  3. Might reduce runners’ susceptibility to patellofemoral disorders (source). 
  4. Can improve running economy and performance in trained runners (read this study). 

Regular running shoes are average in height: not minimalist, not maximalist. They don’t stand out. These shoes are usually very versatile and offer both cushioning and responsiveness. These shoes are the most beginner-friendly. If you’re looking for softer running shoes, keep in mind that the hardness of the midsole does not seem to influence running-related injury risk.

Medium stack height running shoe

Maximal stack height is found in maximalist running shoes. No mistakes here, these shoes are huge. They are recommended for heel strikers, heavier runners, runners looking for extra or plushy cushioning and avoiding any ground feel. Usually used for recovery runs and long runs. 

Maximal stack height running shoe

Good to know if considering maximalist running shoes: 

  1. Choosing a maximalist shoe may be less risky than minimalist shoes when shifting from traditional running footwear, particularly in the initial month of exposure (source). 
  2. Runners who are new to running in a maximal shoe may be at an increased risk of injury as shown in this study.
  3. The eversion mechanics in the maximal shoes from this study may place runners at a greater risk of injury (source). 
  4. Running in highly cushioned shoes increases leg stiffness and amplifies impact loading (explained in this study).
  5. Maximalist running shoes may increase the external impact loading during downhill treadmill running (read more here). 
  6. Highly cushioned shoes did not show immediate changes in running biomechanics (as explained here). 

Carbon plated running shoe with a maximal stack height

A subgroup is made of carbon-plated running shoes - they are also maximalist, but performance-oriented and race-ready. In this case, they are recommended for forefoot strikers and racing.  

How to measure the stack height 

When looking at the brand’s specifications, stack height is sometimes given with and other times without the insole thickness. In our lab, we always include the insole because:

  1. You obviously run with your insoles 
  2. We want consistency in our results 
  3. We measure it the same way for all shoes using World Athletics standards. 

Per rules set by World Athletics, stack height is measured at 12% and at 75% of the inside length of the shoe. In case you want to do it yourself, this is how. 

In our lab where we cut-open shoes to see what’s inside and measure all the possible segments, we also mark the 12% and the 75% of the inside length of the shoe prior to using a caliper. 

Measuring stack height in the lab

Tool: Stack height and heel drop correlation

Heel to toe drop is the difference between heel stack height and forefoot stack height. These two are tightly related and here you can see how: 

Heel drop and stack height

While heel to toe drop varies from 0mm up to 15mm, stack height varies from 3 to 50mm. Here are 4 examples from our lab:

Heel to toe drop vs stack height combinations

Lab insight: We rarely get the same numbers as those specified by the brands. So, take the brand’s numbers with a grain of salt and their marketing intentions on your mind. 

For example, Gaviota 3 has a 5mm drop as per its specifications, but in our lab, we measured almost 10mm. On Cloudswift is said to have a 7mm drop and we measured 11.6mm.

Stack height and ground feel

The amount of cushioning separates running shoes into 4 different categories. These categories don’t only tell us the stack height, but also how much ground feel you can expect. The more you feel the ground, the less you feel the shoe and vice versa. 

This would be rather intuitive if race-ready maximalist shoes haven’t flooded the market. Before that, it was simple: the smaller the stack height, the better the experience for lightweight runners. More stack height and heavier runners can enjoy all the cushioning and not feel dragged down by the shoe’s weight. 

Shoe type Barefoot Minimalist Regular Maximalist Carbon-plated maximalist
Runner's weight Light Lighter Any Heavy Any

Stack height & foot strike correlation

How and where you land while running depends not only on your running form but also on the amount of cushioning in your shoes. There are 3 types of foot strikes: 

  1. Forefoot strike (landing on your toes)
  2. Midfoot strike 
  3. Rearfoot strike (landing on your heel).

It’s best to look for cushioning in the places where you land. 

In our database, the breakdown looks like this: 

  • 42.3% of shoes are made for heel strikers, 
  • 34.1% of shoes are made for all foot strikes, 
  • 23.5% of shoes are made for forefoot and midfoot strikers. 

In general, this is how foot strike relates to stack height: 

  Heel stack height Foot strike
Barefoot shoes 3-8mm Forefoot, midfoot
Minimalist shoes 3-13mm Forefoot, midfoot
Regular shoes 9-29mm All
Maximalist shoes 30mm and up All, but mostly heel strike
Carbon-plated maximalist shoes 30mm and up Forefoot 

Stack height for heel strikers 

Since impact forces are the highest in heel striking, that type of landing asks for the biggest amount of cushioning, i.e. the heel stack height should be high. You can browse shoes for heel strikers here. Also, this is the reason why shoes with lower forefoot stack height (barefoot and minimalist) are usually recommended to the forefoot and midfoot strikers. 

Here's how heel-strike-friendly shoes look like with all that technology in the heel area: 

Running shoes for heel strikers

Running shoes for forefoot strikers don’t get to be so fancy.

Forefoot strikers: the price they have to pay

When talking about stack height, most people assume it’s the heel stack height. Forefoot stack height is often neglected simply because there are much more runners who land on their heel (94% of them as per this study) rather than on their toes. That’s why more people care about heel stack height. 

That would all be ok if there were more shoes aimed at forefoot striking runners but there are not. Usually, we have shoes that work for all strikes and then, based on your personal preferences, you figure out if they work for you. Now we are not taking into account the supershoes (carbon-plated premium race shoes). 

Here are a few examples of running shoes. All of them are advertised for forefoot and midfoot strike only or for all the 3 footstrikes. \

Stack height for forefoot and midfoot strike

Shoes with lower stack height might promote a midfoot or forefoot strike simply because there’s not enough cushion to absorb the impact forces happening when you land on your heel. If you’re a forefoot striker, pay attention to the forefoot stack height. You also might not need to pay for all the features packed at the heel of the shoe. If unsure, look at the collection of running shoes for forefoot and midfoot strike

To learn more about foot strike and its importance for runners, read our in-depth guide on foot strike

Shoe flexibility and stack height 

Across the above-mentioned categories (from barefoot to maximalist), it’s obvious that with the increase in stack height, shoes get stiffer. 

Cushioning type % of all shoes Average heel stack height
Very Flexible 3.2 13.8
Flexible 65.0 26.2
Moderate 23.7 27.5
Stiff 6.3 30.2
Very stiff 1.8 31.2

More midsole material makes the shoes more difficult to bend. Carbon plates add extra stiffness as well. That’s why Saucony Endorphin Pro 2 scored the highest in our lab when doing the flexibility test:

 

Stack height increase analysis (2015-2021)

We looked at the stack height change throughout the years using our full shoe database. We wanted to see whether the shoes are getting higher (we expected so). Thank you, Reddit, for this inspiration!

We took into account only road running shoes. Their release dates were grouped per quarter and we looked only at the 90th percentile value of the stack height so we can see how tall the tallest shoes are getting. 

It was implied that carbon-plated shoes are faulty of this trend, so we also analyzed the stack height without carbon-plated shoes. Turns out, in a world where they did not exist, the stack height trend wouldn’t be much different. 

Stack height trend

Disqualified when higher than 40mm

For recreational runners, there’s no limit in stack height. Currently, it goes as high as 50mm at the heel. However, for competitive runners, especially those aiming for the podium, it’s best to check the regulations of the race in question. Currently, World Athletics has a limit of 40mm in heel stack height for official competitions. 

Anything above means disqualification.

Author
Jovana Subic
Jovana Subic

Whether it's a vertical kilometre or an ultra, climbing in the Alps or exploring local mountains, Jovana uses every opportunity to trade walls and concrete for forests and trails. She logs at least 10h/week on trails, with no off-season, and 4x more on research on running and running shoes. With a background in physics and engineering management, she prefers her running spiced with data.