Time of Death Calculator using Algor Mortis

Forensic Science Tools

This calculator provides an estimate of the post-mortem interval (PMI) based on the principles of Algor Mortis—the cooling of a body after death. By entering the body’s rectal temperature and the ambient (surrounding) temperature, you can get a time-since-death estimation based on the Glaister formula. This tool is intended for educational and informational purposes only and is not a substitute for professional forensic analysis.

Estimated Time Since Death (PMI)

~5.6 Hours

Body Cooling Curve Visualization

Chart showing the estimated decrease in body temperature over time.

Understanding the Science: What is Algor Mortis?

Algor mortis, Latin for “coldness of death,” is the post-mortem process where a body cools to match the temperature of its surroundings. After death, the body’s internal thermoregulation ceases, and it begins to lose heat through processes like radiation, convection, and conduction. This cooling rate is a key piece of information in forensic science for calculating the time of death using algor mortis answers. While it seems straightforward, the rate of cooling is not perfectly linear and can be influenced by numerous factors. However, for initial estimations, a standard rate is often used, which forms the basis of this calculator.

Forensic investigators measure the rectal temperature as it provides the most stable reading of the body’s core temperature. By comparing this to the normal living body temperature (approx. 98.6°F or 37°C) and considering the ambient temperature, they can work backward to estimate the post-mortem interval (PMI). This calculator uses a well-known formula to provide these initial answers.

The Glaister Formula for Calculating Time of Death

The most common and simplified formula used for a basic estimation of the time of death is the Glaister equation. It provides a linear approximation of the cooling process. The formula is:

Time Since Death (in hours) = (Normal Body Temperature – Measured Rectal Temperature) / Cooling Rate

Typically, the ‘Normal Body Temperature’ is assumed to be 98.6°F (37°C), and the ‘Cooling Rate’ is approximated at 1.5°F (0.83°C) per hour. It’s a foundational concept in forensic science for getting a preliminary timeframe.

Variables in the Formula

Variables used in the Glaister equation for calculating the time of death.

Variable	Meaning	Unit	Typical Range
Normal Body Temp	The assumed body temperature of a healthy living human.	°F or °C	98.6°F or 37°C
Measured Rectal Temp	The core body temperature of the deceased at the time of discovery.	°F or °C	Ambient Temp to 98.6°F
Cooling Rate	The estimated rate at which the body loses heat per hour.	°F/hr or °C/hr	~1.5°F/hr (~0.83°C/hr)

Practical Examples of Calculating Time of Death

Example 1: Indoor Discovery

• Inputs:
  • Measured Rectal Temperature: 86.6°F
  • Ambient Temperature: 70°F
  • Unit: Fahrenheit
• Calculation: (98.6°F – 86.6°F) / 1.5°F/hr = 12°F / 1.5°F/hr = 8 hours.
• Result: The estimated time since death is approximately 8 hours.

Example 2: Cooler Environment

• Inputs:
  • Measured Rectal Temperature: 28°C
  • Ambient Temperature: 15°C
  • Unit: Celsius
• Calculation: (37°C – 28°C) / 0.83°C/hr = 9°C / 0.83°C/hr ≈ 10.8 hours.
• Result: The estimated time since death is approximately 10.8 hours.

How to Use This Time of Death Calculator

Follow these steps to get your estimation:

1. Enter Rectal Temperature: Input the measured core temperature of the deceased into the first field.
2. Enter Ambient Temperature: Input the temperature of the environment where the body was located. While the basic Glaister formula doesn’t directly use this, it’s critical for context and more advanced calculations.
3. Select Temperature Unit: Choose whether your input temperatures are in Fahrenheit (°F) or Celsius (°C). The calculator will automatically handle the conversion.
4. Review the Results: The calculator instantly displays the estimated hours that have passed since death. You can also see the total temperature loss and the assumed cooling rate used in the calculation.
5. Interpret with Caution: Remember, this is a simplified estimation. Many factors can alter the actual time of death.

Key Factors That Affect Algor Mortis

The 1.5°F/hr cooling rate is a rule of thumb. In reality, calculating the time of death using algor mortis answers is complex because many variables can speed up or slow down body cooling.

• Clothing and Coverings: Layers of clothing or blankets act as insulation and slow down heat loss significantly.
• Body Mass (BMI): A higher body fat percentage provides more insulation, causing the body to cool slower. A thinner individual will cool faster.
• Air Movement: A body in a windy or drafty area will cool faster due to convection.
• Humidity: Moist air can increase the rate of heat loss compared to dry air.
• Immersion in Water: Water is a much better conductor of heat than air. A body submerged in cool water will lose heat very rapidly, making the standard formula inaccurate.
• Initial Body Temperature: The formula assumes a starting temperature of 98.6°F. If the person had a fever or was suffering from hypothermia at the time of death, the starting point changes, skewing the results.

Frequently Asked Questions (FAQ)

1. How accurate is calculating the time of death with algor mortis?

It is most accurate within the first 12-18 hours after death. After this period, the body temperature gets closer to the ambient temperature, and the margin of error increases significantly. It should be considered an estimation, not an exact science.

2. Why is rectal temperature used?

The rectum provides a consistent and protected area to measure the core body temperature, which is less affected by immediate external conditions than skin temperature.

3. What is the “temperature plateau”?

In the first hour or so after death, the body temperature may not drop noticeably. This is known as the temperature plateau. The body’s large mass takes time to start losing heat externally.

4. Can a body’s temperature increase after death?

Yes, if the ambient temperature is higher than the body’s temperature (e.g., in a desert), the body will absorb heat and its temperature will rise until it equalizes with the environment.

5. Does the ambient temperature change the formula?

Some more advanced formulas, like the Henssge nomogram, use ambient temperature and body weight to create a corrective factor for a more accurate PMI. The simple Glaister formula does not, but knowing the ambient temperature is crucial for a forensic expert to judge the validity of the estimate.

6. Why does the calculator have an input for ambient temperature if the formula doesn’t use it?

It’s included for completeness and as a reminder that it’s a critical factor in real-world forensic analysis. The cooling chart also uses it to show the temperature floor.

7. Can this calculator be used for legal purposes?

Absolutely not. This is an educational tool only. Estimating time of death for legal or investigative purposes must be done by a qualified forensic professional who considers all influencing factors.

8. What other ‘mortis’ types are there?

The other two classic signs of death are livor mortis (pooling of blood causing discoloration) and rigor mortis (stiffening of the muscles). All three are used together to narrow down the PMI.