Algor Mortis Calculator: Calculating Time of Death
Estimate the Post-Mortem Interval (PMI) using body and environmental temperature.
The internal temperature of the body when discovered.
The temperature of the surrounding environment (air, water, etc.).
Select the unit for the temperatures entered above.
Post-Mortem Cooling Analysis
| Hours Since Death | Estimated Body Temperature |
|---|---|
| Enter values and calculate to generate the cooling schedule. | |
What is Activity 11-2: Calculating Time of Death Using Algor Mortis?
“Activity 11-2: Calculating time of death using algor mortis” refers to a common forensic science exercise focused on estimating the Post-Mortem Interval (PMI), which is the time that has elapsed since a person has died. Algor mortis, or “death chill,” is the process by which a body cools after death until it reaches the ambient temperature of its surroundings. By measuring the body’s temperature and the environmental temperature, investigators can work backward to estimate when death occurred. This calculator automates the process, primarily using the Glaister equation, a foundational formula in forensics.
This estimation is a critical first step in many death investigations, helping to establish a timeline of events. However, it’s important to understand that algor mortis is an estimation, not an exact science, as many factors can influence the cooling rate.
The Formula for Calculating Time of Death (Glaister Equation)
The most common formula used for a basic estimation of the time of death from algor mortis is the Glaister equation. It provides a simple linear model for body cooling. The standard formula assumes a normal living body temperature of 98.6°F (37°C).
This equation posits that a body will lose approximately 1.5°F per hour. While simple, it serves as a valuable starting point for forensic analysis.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Normal Body Temp. | The assumed body temperature at the time of death. | °F or °C | 98.6°F (37°C) |
| Measured Rectal Temp. | The core body temperature measured at the scene. | °F or °C | Ambient Temp. to 98.6°F |
| Cooling Rate | The rate at which the body is assumed to lose heat. | Degrees per Hour | ~1.5°F/hr or ~0.78°C/hr |
Practical Examples
Example 1: Standard Indoor Scenario
- Inputs: A body is found indoors. The rectal temperature is 86.6°F, and the room’s ambient temperature is a stable 72°F.
- Calculation:
- Temperature loss = 98.6°F – 86.6°F = 12.0°F
- Hours since death = 12.0°F / 1.5°F per hour = 8 hours
- Result: The estimated time of death is approximately 8 hours prior to the discovery. This is a classic application of calculating time of death using algor mortis.
Example 2: Colder Environment (Celsius)
- Inputs: A body is discovered outside. The rectal temperature is 28°C, and the ambient air temperature is 10°C.
- Unit Conversion: First, convert to Fahrenheit for the standard formula. Normal temp is 37°C.
- Temperature loss = 37°C – 28°C = 9°C
- Convert cooling rate to Celsius: 1.5°F/hr is roughly 0.83°C/hr. A more direct source states 0.78°C/hr. Let’s use that.
- Hours since death = 9°C / 0.78°C per hour ≈ 11.5 hours
- Result: The estimated time of death is approximately 11.5 hours ago.
How to Use This Time of Death Calculator
- Enter Rectal Temperature: Input the core body temperature measured at the scene into the first field.
- Enter Ambient Temperature: Input the temperature of the surrounding environment.
- Select Units: Choose whether you are using Fahrenheit (°F) or Celsius (°C). The calculator will handle any necessary conversions.
- Calculate: Click the “Calculate” button to see the estimated time since death.
- Review Results: The calculator displays the primary result (hours since death) and intermediate values like total temperature loss. The chart and table below provide a visual representation of the cooling process.
Key Factors That Affect Algor Mortis
The 1.5°F/hour rule is a guideline. The actual rate of cooling when calculating time of death using algor mortis can be faster or slower due to several factors:
- Clothing/Insulation: Layers of clothing or blankets act as insulation and slow down the cooling process significantly.
- Environmental Temperature: A larger difference between the body and ambient temperature leads to a faster initial cooling rate.
- Body Fat and Size: Individuals with a higher body fat percentage or larger body mass will cool slower than smaller, leaner individuals.
- Air Movement: Wind or drafts increase heat loss through convection, speeding up the cooling process.
- Immersion in Water: Water is a much better conductor of heat than air. A body in water will cool 3-4 times faster than a body in air of the same temperature.
- Initial Body Temperature: The formula assumes a normal temperature of 98.6°F, but the person could have had a fever (hyperthermia) or been in cold conditions (hypothermia) at the time of death, altering the starting point.
Frequently Asked Questions (FAQ)
- 1. How accurate is calculating time of death using algor mortis?
- It is an estimate. Under ideal conditions, it can be fairly accurate in the first 12-18 hours. However, due to the many variables, it is rarely used as the sole determinant of the PMI.
- 2. What is the Glaister equation?
- It is the formula this calculator is based on: Hours since death = (98.6°F – rectal temp) / 1.5. It’s a foundational but simplified model for estimating the post-mortem interval.
- 3. Does the formula change after 12 hours?
- Yes, some models use a two-stage cooling rate. A common variation suggests a rate of ~1.5°F/hour for the first 12 hours, and then a slower rate of ~1.0°F/hour after that as the body temperature gets closer to ambient.
- 4. Why is rectal temperature used?
- Rectal or liver temperature provides a measure of the body’s core temperature, which is more stable and cools more predictably than skin temperature.
- 5. What happens if the body temperature is the same as the ambient temperature?
- Once the body reaches thermal equilibrium with its environment, algor mortis can no longer be used to estimate the time of death. This indicates a longer post-mortem interval.
- 6. Can a body’s temperature increase after death?
- Yes, if the ambient temperature is significantly higher than body temperature (e.g., in a desert or a hot car), the body will absorb heat and its temperature will rise to match the environment.
- 7. What other methods are used to determine time of death?
- Forensic investigators also use rigor mortis (stiffening of muscles), livor mortis (settling of blood), and entomology (insect activity) to build a more accurate timeline.
- 8. Is this calculator a valid tool for legal investigations?
- No. This tool is for educational and illustrative purposes only. A true forensic estimation requires physical examination by a trained professional who can account for all environmental and bodily factors.
Related Tools and Internal Resources
For more detailed analysis, explore these related forensic science topics: