Drop is the height difference between the heel and the forefoot of a running shoe, measured in millimetres. A shoe with 34mm of foam under the heel and 26mm under the forefoot has an 8mm drop. That is the entire definition, and it is one of the few numbers on a spec sheet that changes where the work goes in your legs.
Two shoes can weigh the same, cost the same and feel equally soft when you squeeze them, and still ask very different things of your calves. That difference is drop. It is worth understanding before you change it, because changing it carelessly is one of the more reliable ways to injure yourself.
What the number is, and what it is not
Stack height is how much material sits between your foot and the ground. Running shoe drop is simply the gap between the heel stack and the forefoot stack. The two measurements move independently, and that is what catches people out.
A shoe can be enormously thick and still have a 4mm drop. A thin, firm racing flat can have a 10mm drop. Plenty of runners assume low drop means minimal and high drop means cushioned, and neither is true. If you want to know how much shoe is under you, read the stack height. If you want to know how the shoe angles your foot, read the drop.
Treat the published figure as approximate. Brands do not all measure the same way, and whether the insole is included shifts the number a little. A 1mm difference between two shoes is noise. A 6mm difference is something your Achilles will notice by the end of the first week.
What actually changes when the drop changes
Raising the heel relative to the forefoot tilts you slightly forward and shortens the range the ankle has to travel through on each step. Load shifts up the chain, towards the knee. It also makes life easier if you land heel first, which most recreational runners do, because the heel meets the ground with material already under it.
Lowering the drop does the opposite. The ankle travels through more range, the foot lands flatter, and the calf and Achilles take a larger share of the work. That is not a fault. A well conditioned calf complex handles it happily, and some runners genuinely feel smoother in a low drop shoe. But it is more work for tissue that is already the most commonly aggravated area in distance running.
Neither end of the scale is superior. There is no correct drop in the abstract, only the drop your legs are currently conditioned for. Runners who have had recurring knee irritation sometimes find a higher drop more comfortable, and runners who have had Achilles trouble sometimes find the opposite; comfort is the honest way to describe that, not treatment. If something actually hurts, see a physiotherapist rather than shopping for a fix.
A rough guide to the bands
| Drop | Usually called | Loads more towards | Typically suits |
|---|---|---|---|
| 0-4mm | Low or zero drop | Calf, Achilles, ankle | Midfoot and forefoot landers with conditioned calves |
| 5-7mm | Mid drop | Fairly balanced | Most runners, and anyone unsure where to start |
| 8-10mm | Traditional | Knee and quad | Heel strikers, higher mileage, tight calves |
| 11mm and up | High drop | Knee and quad | Pronounced heel strikers, runners used to it already |
Most of the running shoes sold in the UK sit between 6mm and 10mm, which is not an accident. That range works for the largest number of people with the fewest complaints.
The bit that actually causes the injuries
Here is the plain version, and it is the most useful sentence in this article: going straight from a 10mm shoe to a 4mm shoe and running your normal week is a classic route to Achilles tendon pain and calf strains. It happens every year, to sensible people, usually within a fortnight of a new pair arriving.
The shoe is not defective. The tissue simply has not been asked to work through that range at that volume before. Tendons adapt slowly, considerably more slowly than the muscles around them, so the first week can feel fine and the problem shows up in week three.
If you want to drop down, do it like this:
- Keep your current shoes. You are adding a pair, not replacing one.
- Run one short, easy run a week in the lower drop shoe for the first two weeks.
- Add a second easy run per week, then build over roughly six to eight weeks.
- Expect mild calf tightness. Do not push through sharp or localised Achilles pain, which is the signal to go back a step.
- Do not change drop and start a speed block in the same month. If something flares up you will not know which one did it.
- Never debut a new drop on race day.
Going the other way, from low to high, is usually less dramatic, but it is still a change and it still deserves a couple of easy runs before a long one.
How to decide without overthinking it
If you are running comfortably and injury free, the simplest answer is to note the drop of the shoe you are getting on with and stay near it. Replacing a shoe you love with the closest thing to it is a boring strategy that works.
If you are buying your first proper pair, start in the middle of the range and let comfort decide between the options in front of you. Comfort on the run is a better guide than any number, and it is the one thing you cannot read off a website. Ten minutes with someone who watches you run beats an afternoon of spec sheets, so a gait analysis or a proper in-store fitting is worth the trip.
If you rotate two pairs, having a small difference in drop between them is a reasonable idea, because it varies the load slightly rather than hammering the same tissue every session. Small, though. A 2 or 3mm gap, not 8. The rest of the running range is worth a look once you know which end of the scale you belong at.
And if all of this feels like a lot of detail for one measurement, that is a fair reaction. Drop matters most at the moment you change it. The rest of the time, it quietly does its job.