This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.
How the body cools after death
After death, heat production stops and the body gradually cools toward the temperature of its surroundings. This cooling is called algor mortis. Measuring the core temperature, usually in the rectum, is one of the oldest ways to estimate the time since death, also called the postmortem interval.
The Glaister rule
The classic rule, attributed to the Scottish forensic scientist John Glaister, assumes a loss of about 1.5 °F (0.83 °C) per hour:
Hours since death ≈ (98.7 °F − rectal temperature in °F) ÷ 1.5
A body at 92.7 °F suggests about (98.7 − 92.7) ÷ 1.5 = 4 hours. If the temperature was measured at 10:00 AM, death would have occurred around 6:00 AM.
Why it is only a rough guide
- Plateau: for the first 30 minutes to a few hours, the core temperature barely falls.
- Environment: a cold room, wind, water or wet clothing speed up cooling; blankets, clothing and a warm room slow it down.
- Body size: a heavy body cools more slowly than a thin one or a child.
- Starting temperature: fever, hypothermia or intense exertion before death change the starting point.
Forensic doctors therefore use the Henssge nomogram, which accounts for the ambient temperature and body weight, with correction factors for clothing and air movement. Even then, the uncertainty is often 3 hours or more.
Other signs
| Sign | Typical timing |
|---|---|
| Livor mortis (lividity) | appears within 20 minutes to 2 hours, fixed after about 8 to 12 hours |
| Rigor mortis | starts at 2 to 6 hours in the jaw and neck, complete at 6 to 12 hours, resolves after 24 to 48 hours |
| Corneal clouding | a few hours with the eyes open |
| Decomposition | from about 2 to 3 days, much faster in heat |
All these timings vary with temperature: heat speeds them up, cold slows them down.
Important
This calculator is for education, crime fiction and curiosity. Only a doctor can certify a death, and the postmortem interval in a real case is established by forensic specialists combining many findings. If you find someone who appears to be dead, call 911.