How accurate is temperature-based PMI estimation?

The Henssge nomogram achieves ±2.8 hours accuracy (95% CI) within the first 24 hours postmortem under standard conditions. Accuracy decreases after 24 hours as the body approaches ambient temperature. Environmental variables (wind, rain, heating) reduce accuracy further.

Why use rectal temperature specifically?

Rectal temperature most closely reflects core body temperature, which is the basis of the Henssge model. Brain (tympanic) or hepatic temperatures can be used but have different cooling curves. Rectal temperature is the standard in forensic practice and is the temperature the nomogram was validated with.

What is the initial temperature plateau?

After death, body temperature remains relatively stable for 30-90 minutes before linear cooling begins. This "sigma phenomenon" is due to residual metabolic heat, thermal inertia, and ongoing enzymatic reactions. The double-exponential model accounts for this plateau; simple Newton's law does not.

Does fever before death affect the estimate?

Yes. The model assumes a starting body temperature of 37.2°C. If the person had a fever (39-40°C), the PMI will be underestimated. Similarly, hypothermia before death overestimates PMI. Adjusting the baseline temperature improves accuracy when antemortem temperature is known.

Can this be used for bodies found in water?

Bodies in water cool approximately twice as fast as in air at the same temperature. The water correction factor (0.5) partially accounts for this, but accuracy in aquatic environments is reduced compared to indoor scenes. Current, water temperature variability, and clothing significantly affect cooling.

What other methods are used alongside body cooling?

Forensic pathologists use multiple modalities: rigor mortis progression (2-12 hours onset, 24-36 hours resolution), livor mortis fixation (8-12 hours), vitreous potassium concentration, gastric contents analysis, entomological evidence (insect activity), and scene investigation findings.

Time of Death Estimator — Postmortem Interval (PMI) Calculator

Estimate time since death with a simplified Henssge-based body-cooling worksheet that also shows broad postmortem-change timelines.

⚠️ Forensic/Educational Tool: This calculator provides estimates based on the Henssge nomogram and Newtonian cooling models. Actual postmortem interval estimation requires expert forensic pathology evaluation with multiple corroborating methods. Results are approximations only.

Temperature Measurements

Temperature Unit

Rectal (Core) Temperature (°C)Measured at scene

Ambient Temperature (°C)Environmental temperature at scene

Body & Environment Factors

Body Weight (kg)

Clothing / Covering

Body Build

Body Surface / Environment

Estimated Time Since Death

0.6 hours

Range: 0.5–0.7 h (±15%)

Cooling Rate

12.21 °C/h

Average observed rate

Correction Factor

Weight × clothing × build × surface

Temperature Ratio (Q)

0.581

Body 30°C / Ambient 20°C

Rigor Mortis

Not yet present

At ~0.6 h postmortem

Livor Mortis

Absent or minimal

Gravity-dependent discoloration

Postmortem Changes Timeline

Time (hours)	Body Temperature	Rigor Mortis	Livor Mortis	Other Signs
0–2	Initial plateau (37–36°C)	Absent	Minimal	Corneal clouding begins
2–6	Linear cooling (~1°C/h)	Developing (jaw → limbs)	Developing, blanches	Drying of exposed mucosa
6–12	Continued cooling	Full rigor	Partially fixed	Potassium rise in vitreous
12–24	Approaching ambient	Begins resolving	Fixed	Early color changes
24–48	At/near ambient	Mostly resolved	Fixed	Green discoloration (abdomen)
48–72+	At ambient	Absent (secondary flaccidity)	Fixed	Bloating, marbling, skin slip

Corrective Factors Reference

Condition	Multiplier	Effect on Cooling
Naked body	0.35	Cools faster
Light clothing	0.5	Slightly faster
Normal clothing	0.7–1.0	Standard
Heavy clothing + bedding	1.4–1.8	Cools slower
Body in water	0.5	Much faster
Obese body habitus	1.2	Cools slower
Thin body habitus	0.85	Cools faster

Planning notes, formulas, and examples

About the Time of Death Estimator — Postmortem Interval (PMI) Calculator

Estimating the time since death — the postmortem interval (PMI) — is a standard part of forensic pathology and medicolegal death investigation. One of the most commonly used early approaches is algor mortis: the cooling of the body after death. The Henssge nomogram is a reference approach that models this cooling with a double-exponential curve rather than a simple straight line.

This page implements a simplified Henssge-based worksheet using core temperature, ambient temperature, body weight, clothing, body build, and environment adjustments. It provides an educational PMI estimate with a broad uncertainty range rather than a formal forensic opinion.

The postmortem-change table is included as supporting context only. In real casework, scene information, body handling history, and other forensic findings matter alongside temperature.

When This Page Helps

PMI estimation helps organize timelines, compare witness statements, and narrow an initial review window. This worksheet is best used for forensic education and preliminary scene review rather than as a substitute for a formal medicolegal opinion.

How to Use the Inputs

Enter the rectal (core) temperature measured at the scene in °C or °F.
Enter the ambient temperature of the environment where the body was found.
Enter body weight in kilograms.
Select the clothing/covering level — from naked to heavy clothing with bedding.
Select body build (thin, normal, obese) and body surface type.
Review the estimated time since death, cooling rate, and postmortem changes timeline.

Formula used

Henssge double-exponential: Q = (T_rectal − T_ambient) / (37.2 − T_ambient) = 1.25 × e^(-kt) − 0.25 × e^(-5kt)
Cooling constant k = 1.2815 / (corrective_factor)
Corrective factor = clothing × mass_factor × build_adj × surface_adj
Solved iteratively for time t (hours)

Example Calculation

Result: Estimated PMI: ~8.5 hours (range 7.2–9.8 h)

Body cooling from 37.2°C to 30°C in a 20°C environment with standard correction factor ~1.0 yields a temperature ratio Q of 0.59. Solving the double-exponential equation gives approximately 8.5 hours postmortem, with a ±15% confidence interval of 7.2 to 9.8 hours.

Tips & Best Practices

Measure rectal temperature as early as possible at the scene — delay reduces accuracy as the body continues cooling.
Record ambient temperature at body level, not room thermostat reading — floor temperatures can differ dramatically from room center.
Consider antemortem conditions: fever, hypothermia, intense exercise, or drug effects on thermoregulation can shift the baseline.
In outdoor scenes, ambient temperature may have varied (day/night cycles) — use average estimated temperature for the relevant period.
Always use multiple PMI estimation methods (temperature + rigor + livor + scene evidence) — no single method is sufficient alone.

Practical Guidance

Use consistent units, verify assumptions, and document conversion standards for repeatable outcomes.

Common Pitfalls

Most mistakes come from mixed standards, rounding too early, or misread labels. Recheck final values before use.

Practical Notes

Keep assumptions explicit and treat the result as a worksheet estimate, not a substitute for a full forensic review.

Sources & Methodology

Last updated: March 28, 2026

Methodology

This page uses a simplified Henssge-style body-cooling worksheet. It combines core temperature, ambient temperature, body weight, clothing, body habitus, and surface or environment adjustments to estimate a postmortem interval from cooling, then places that estimate beside standard rigor and livor timelines.

It is not a forensic report. Real postmortem interval work requires scene information, body handling history, environmental variation, and other postmortem findings in addition to temperature.

Sources

Temperature based forensic death time estimation: The standard model in experimental test (PubMed / Legal Medicine) — Experimental validation paper describing the Henssge standard model for temperature-based postmortem interval estimation.
Death time estimation in case work. II. Integration of different methods (PubMed / Forensic Science International) — Classic reference emphasizing that temperature must be integrated with other forensic findings.

Frequently Asked Questions

The Henssge nomogram achieves ±2.8 hours accuracy (95% CI) within the first 24 hours postmortem under standard conditions. Accuracy decreases after 24 hours as the body approaches ambient temperature. Environmental variables (wind, rain, heating) reduce accuracy further.