Stack height is the total thickness of material between the bottom of your foot and the ground, measured in millimeters. It includes the insole, midsole, and outsole combined. A shoe with 6mm of stack height puts you close to the ground. A shoe with 33mm of stack height has significant cushioning underfoot.
Why Stack Height Matters
Stack height determines two things: how much cushion sits between you and the ground, and how much ground feel you get. Lower stack means more proprioception — your feet can sense terrain, texture, and slope. Higher stack means more protection and cushioning, but less sensory feedback.
For zero drop shoes specifically, stack height is what separates a minimal barefoot shoe from a maximally cushioned one. Both can have zero heel-to-toe drop, but the experience of wearing them is completely different.
Stack Height Ranges
Minimal (4-12mm) — True barefoot-style shoes. You feel everything underfoot — pebbles, roots, pavement texture. Brands like Vivobarefoot and Xero Shoes focus here. Best for people who want maximum ground feel and have adapted feet.
Moderate (13-22mm) — A middle ground with some cushion but decent ground feel. Good for transitioning runners and people who want barefoot mechanics without the intensity of minimal shoes. Many Merrell and Inov-8 models land here.
Max cushion (23-35mm+) — Thick cushioning with zero drop. Altra pioneered this with models like the Olympus and Paradigm. Popular with ultrarunners and people who want a level platform with maximum protection for long distances.
Stack Height and Stability
Higher stack height raises your center of gravity, which can reduce stability on uneven terrain. This is why most trail running shoes keep stack height moderate — a 30mm+ stack on rocky singletrack creates more ankle roll risk than a 15mm stack.
On roads and smooth surfaces, high stack height is less of a stability concern. The flat, predictable surface compensates for the raised platform.
Stack Height and Ground Feel
Ground feel decreases as stack height increases. This matters because proprioception — your brain's awareness of foot position and terrain — relies on sensory feedback from the soles of your feet.
With 6mm of stack, you can feel the difference between grass and pavement. With 30mm, you mostly feel cushion. Neither is wrong, but they serve different purposes. Minimalists prioritize sensory connection. Maximalists prioritize comfort over distance.
Choosing Your Stack Height
Go minimal (4-12mm) if you: - Want maximum ground feel and proprioception - Have strong, adapted feet from barefoot training - Run shorter distances or walk primarily - Prefer feeling connected to the terrain
Go moderate (13-22mm) if you: - Are transitioning from conventional shoes - Run moderate distances (5K-half marathon) - Want some cushion without losing all ground feel - Run mixed terrain (roads and light trails)
Go max (23-35mm) if you: - Run ultramarathons or high weekly mileage - Want zero drop benefits with conventional-level cushioning - Have joint concerns that benefit from more material underfoot - Run primarily roads or smooth trails
Stack Height by Activity
| Activity | Recommended Stack | Why |
|---|---|---|
| Daily walking | 6-15mm | Ground feel for proprioception, foot strengthening |
| Road running | 15-30mm | Cushion for repetitive pavement impact |
| Trail running | 12-25mm | Balance of protection and stability |
| Hiking | 15-25mm | Protection from rocks with trail stability |
| Casual wear | 6-15mm | Comfort and foot strengthening all day |