What is a crowd crush, and how do you calculate safe density?

Most people picture a "stampede" when they hear about a fatal crowd incident — people running, trampling each other underfoot. Almost every real crowd disaster looks nothing like that. The mechanism that actually kills people is called crowd crush, and it can happen in a totally silent, motionless crowd. Understanding how it works is the single most useful thing an event organiser can learn.

What actually happens in a crowd crush

A crowd crush isn't people trampling each other. It's compressive asphyxia — so many bodies packed into so little space that the chest can no longer expand to breathe. At high enough density, a crowd behaves less like a group of individuals and more like a fluid under pressure. Forces from one side of a packed area transmit through bodies to the other side, sometimes strong enough to bend steel barriers. A person can be upright, unable to fall, and still be crushed to death, because there is no way to expand their ribcage against the pressure around them.

This is why crowd crush victims are so often found still standing, or are pulled out of a crowd that looks — from a distance — calm. The people at the edge of a packed crowd frequently have no idea anyone in the middle is dying.

The density numbers that matter

Crowd density is measured in people per square metre. It is the single most important number in crowd safety, and it has well-established thresholds:

• Up to 2 people/m²: comfortable. People can move freely, choose their own pace and direction.
• 2–4 people/m²: packed but generally still manageable — this is normal for the front of a concert or a busy market. Movement becomes difficult and involuntary contact is constant.
• 4–5 people/m²: the danger zone. Individual movement is no longer possible — you move only when the crowd around you moves. This is the threshold at which organisers must actively intervene.
• 5–7 people/m²: dangerous. The crowd moves as a single mass. People can be lifted off their feet by pressure alone. Falls are catastrophic because there's no room to get back up.
• 7+ people/m²: critical. This is the density at which fatal crushes occur. The compressive force is enough to cause injury and asphyxiation even without anyone falling.

For comparison: a crowded rush-hour train carriage is typically around 4–6 people/m². Multiple recent fatal crowd crushes — including events in Mexico, South Korea and Germany over the past two decades — occurred in the 6–10 people/m² range in the area where deaths occurred, even though the wider crowd was far less dense.

How to calculate a safe capacity for your event

The calculation itself is simple. It's the discipline of using it — and enforcing it — that's hard.

Step 1: measure your usable area. Not the total floor space of the venue — the area people can actually stand in, once you subtract the stage, bars, barriers, merchandise stalls and any fixed structures.

Step 2: choose your target density. For a standing concert or festival crowd, 2 people/m² is the widely used planning figure for a "packed but safe" target. For a seated or circulation space, use a lower figure — around 1–1.5 people/m².

Step 3: multiply. Usable area (m²) × target density (people/m²) = your safe capacity.

A 400m² usable space at 2 people/m² gives a safe capacity of 800 people. That's your hard cap — the number you enforce at the gate, not a target you aim to reach and then keep letting people in past.

You can run this calculation instantly with our free crowd capacity calculator, which also flags where your event sits against Martyn's Law thresholds.

Why calculating capacity isn't enough on its own

A safe capacity number is only useful if three other things are also true: you're counting people in and out in real time, you have a plan to stop entry before you hit the number (not after), and someone with real authority is watching density on the ground and empowered to act on what they see. Venues that have all four — the number, the count, the stop-point and the person — very rarely have crowd crush incidents. Venues that have only the number on a piece of paper regularly do.

This is the core of what crowd safety training actually teaches: not just how to do the maths, but how to recognise dangerous density in a real crowd before a spreadsheet would have told you it was a problem, and what to do about it once you have.

Our Festival & Crowd Safety certificate covers density recognition, intervention thresholds and evacuation planning in a 15-minute course. If you're responsible for a whole team, CrowdCert Teams lets you train and certify everyone from one dashboard.