Zombie maths: a serious treatment of an unserious subject
Zombie cinema has been with us since George Romero\'s Night of the Living Dead in 1968, and during five decades the genre has refined the concept significantly. Modern depictions split roughly into three categories:
- Romero classics: shambling undead, must destroy the brain, hungry but slow.
- Fast infected: Danny Boyle\'s 28 Days Later, the World War Z film. Athletic, virally driven, often actually-still-alive.
- Fungal/cordyceps: The Last of Us. Infected hosts retain biological metabolism — they really do starve.
Energy needs of an active zombie
Treating zombies as living humans with reduced cognition: a continuously-moving adult burns roughly 2,500 kcal/day. Add 30% for the inefficiency of constant low-grade activity (no rest cycles) and you reach 3,250 kcal/day. We use 2,500 in the calculator as a baseline — many film zombies are simply not that active most of the time.
Human body as food energy
| Body composition | Energy |
|---|---|
| Adipose tissue (fat) | 9,000 kcal/kg |
| Muscle | 1,800 kcal/kg |
| Organs (liver, heart, kidneys) | 1,500 kcal/kg |
| Bone (mostly mineral) | ~0 kcal/kg |
| Average human total | ~1,800 kcal/kg |
The averaging assumes a typical body composition of 60% water, 20% fat, 15% lean tissue, 5% bone. Higher body fat increases total energy considerably — at 35% body fat, a 75 kg adult would contain closer to 175,000 kcal (about 70 zombie-days).
How long does the apocalypse really last?
A 10,000-strong zombie horde burns 25 million kcal/day. The entire human population of London (9 million) would feed that horde for about 50 days at typical body energy. The maths suggests that a sustained zombie apocalypse hits its own population ceiling fairly quickly — eventually the food runs out and the zombies themselves starve (in canons where biology matters).
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