Algor Mortis Calculator for Calculating Time of Death

An expert tool to estimate the post-mortem interval (PMI) based on body temperature.

Cooling Curve Visualization

Estimated cooling curve based on inputs. The red dot indicates the measured temperature and the calculated time since death.

What is the Algor Mortis Time of Death Calculation?

Algor mortis, Latin for “coldness of death,” is the process by which a body cools after death until it reaches the ambient temperature of its surroundings. Calculating time of death using algor mortis is a fundamental technique in forensic science to estimate the Post-Mortem Interval (PMI). After death, the body’s internal thermoregulation ceases, and it begins to lose heat. This cooling follows a predictable, albeit variable, pattern that can be modeled mathematically.

This calculator uses a simplified version of the Glaister equation, a well-known formula in forensics for this purpose. It’s a crucial tool for investigators, but it’s important to understand that it provides an *estimate*, not an exact time. Many factors can influence the cooling rate, which is why a thorough investigation considers other evidence alongside this calculation.

The Algor Mortis Formula (Glaister Equation)

The most common and straightforward formula for calculating time of death from body temperature is the Glaister equation. While more complex models like the Henssge Nomogram exist, the Glaister formula provides a solid initial estimate, especially in the first 12-18 hours post-mortem.

The formula is expressed as:

Time Since Death (Hours) = (Normal Body Temperature - Measured Rectal Temperature) / Cooling Rate

Our calculator adapts this formula based on the selected units (°C or °F).

Variables in the Algor Mortis Calculation

Variable	Meaning	Unit (Auto-Inferred)	Typical Value / Range
Normal Body Temp	The assumed core body temperature at the time of death.	°C or °F	37°C / 98.6°F
Measured Rectal Temp	The actual measured core temperature of the deceased.	°C or °F	Ambient to Normal Body Temp
Cooling Rate	The rate at which the body is assumed to lose heat per hour.	Degrees per hour	~0.83°C/hr or ~1.5°F/hr

Practical Examples

Example 1: Indoor Discovery

An individual is found deceased in a climate-controlled apartment.

• Inputs:
  • Measured Rectal Temperature: 89.6°F
  • Ambient Temperature: 70°F
  • Units: Fahrenheit
• Calculation:
  • Temperature Drop: 98.6°F – 89.6°F = 9.0°F
  • Estimated Hours: 9.0°F / 1.5°F/hr = 6 hours
• Result: The estimated time since death is approximately 6 hours.

Example 2: Outdoor Scenario (Celsius)

A body is discovered in a shaded, wooded area in the morning.

• Inputs:
  • Measured Rectal Temperature: 28°C
  • Ambient Temperature: 15°C
  • Units: Celsius
• Calculation:
  • Temperature Drop: 37°C – 28°C = 9°C
  • Estimated Hours: 9°C / 0.833°C/hr ≈ 10.8 hours
• Result: The estimated time since death is approximately 10.8 hours. For more complex scenarios, see our guide on the key factors affecting PMI.

How to Use This Algor Mortis Calculator

Follow these steps for an accurate estimation:

1. Select Temperature Unit: First, choose whether you are working with Celsius (°C) or Fahrenheit (°F). All inputs and results will conform to this unit.
2. Enter Measured Rectal Temperature: Input the core body temperature of the deceased as accurately as possible.
3. Enter Ambient Temperature: Input the temperature of the environment where the body was located.
4. Review the Results: The calculator will instantly provide the estimated time since death in hours. It also shows intermediate values like the total temperature drop and the cooling rate used.
5. Interpret the Chart: The cooling curve visualizes the estimated temperature decline over time, helping you understand the context of your result.

Key Factors That Affect Algor Mortis

The simple formula for calculating time of death using algor mortis is a starting point. Forensic experts must consider numerous variables that can alter the cooling rate:

• Clothing/Coverings: Layers of clothing or blankets act as insulation, significantly slowing heat loss.
• Body Mass (BMI): Individuals with a higher body fat percentage will cool more slowly than leaner individuals due to fat’s insulating properties.
• Ambient Temperature: A larger difference between body and ambient temperature leads to a faster initial cooling rate.
• Environment (Air vs. Water): A body submerged in water will lose heat much faster (2-3 times) than a body in air.
• Air Movement: Wind or drafts increase heat loss through convection, accelerating cooling.
• Surface Contact: Lying on a cold, conductive surface (like concrete or tile) will draw heat out of the body faster than a non-conductive surface (like a carpet).
• Initial Body Temperature: The formula assumes a normal temperature at death. A person who died with a high fever or in a state of hypothermia will have a different starting point.

For more details, see our article on understanding taphonomy.

Frequently Asked Questions (FAQ)

1. How accurate is calculating time of death with algor mortis?
It is an estimate. In controlled conditions, it can be quite accurate in the first 12-18 hours. However, the numerous environmental and individual factors mean the result should be corroborated with other methods like rigor mortis and livor mortis analysis.

2. Why is rectal temperature used?
Rectal temperature is the standard because it provides a stable and reliable measurement of the body’s core temperature, which is less affected by immediate external conditions than surface temperature.

3. What if the measured body temperature is higher than normal?
This could indicate the person died with a fever (hyperthermia), or that the ambient environment is extremely hot. The calculator will indicate an error or zero time passed, as the body cannot cool from a temperature it never reached.

4. What if the body temperature is the same as the ambient temperature?
This means the body has reached thermal equilibrium with its environment. Algor mortis calculation is no longer useful, as the cooling process is complete. This indicates a much longer post-mortem interval, likely more than 24-36 hours.

5. Does the cooling rate ever change?
Yes. The rate of 1.5°F/hr is an average for the initial period. The body’s cooling actually follows a sigmoid (S-shaped) curve, with an initial plateau, a period of faster cooling, and then a slowing rate as it approaches ambient temperature. This calculator uses a linear approximation for simplicity.

6. Can I use this calculator for bodies found in water?
This specific calculator is not calibrated for submersion. The cooling rate in water is significantly faster and requires a different formula or correction factor.

7. What other methods complement algor mortis?
Forensic investigators use a combination of algor mortis, livor mortis (settling of blood), and rigor mortis (stiffening of muscles) to narrow down the time of death. Forensic entomology (the study of insects) is also critical for longer PMIs.

8. Does body weight matter?
Yes. Body weight, and more specifically body fat, is a major factor. The formulas used in more advanced tools like the Henssge nomogram include a correction factor for body weight. This calculator provides a general estimate without that specific correction.