Each calculator here is a published peer-reviewed model, implemented from the original equations and verified against the reference values in its source standard. The maths runs on our servers. You enter conditions in the browser, the server returns the trajectory, the page renders it.
The models are zero-dimensional and compartmental. They treat the body as a small number of well-mixed lumps (core and skin, or several body segments) and integrate the heat balance equations forward in time. They are not finite-element simulations of individual tissues. They are the standard tools used in occupational heat science, thermal comfort research, and altitude medicine.
Predicted Heat Strain (PHS)
One-minute time-stepped model of rectal temperature, sweat rate, water loss, and maximum allowable exposure time for a clothed worker in a hot environment.
ISO 7933:2018 (revised 2023). Malchaire et al. 2001. Ioannou et al. 2019.
Open calculatorTwo-node model (Gagge)
Core and skin compartments with separate heat balance equations. Underlies the Standard Effective Temperature used in indoor thermal comfort science.
Gagge, Stolwijk, Nishi 1971. ASHRAE Standard 55.
Open calculatorUTCI
Universal Thermal Climate Index. Derived from a 12-segment Fiala multi-node model and validated against synoptic weather data. Single-number outdoor heat stress metric.
Jendritzky et al. 2012. Fiala et al. 2012.
Open calculatorWBGT
Wet-bulb globe temperature. The occupational standard for heat stress, used by every national heat-safety code in the world. Simpler index, included for reference.
ISO 7243:2017. Yaglou and Minard 1957.
Open calculatorIREQ and Dlim
Required clothing insulation and maximum exposure time before the body cannot maintain heat balance. The cold equivalent of PHS.
ISO 11079:2007. Holmér 1984.
Open calculatorWindchill
Equivalent skin-cooling temperature for any combination of air temperature and wind speed. Gives time to skin freezing on unprotected faces.
Osczevski and Bluestein 2005.
Open calculatorOxygen cascade
Inspired, alveolar, and arterial oxygen partial pressures as a function of altitude. The starting point for understanding why hypoxia produces every symptom of altitude illness.
West et al. textbook physiology. Standard atmosphere.
Open calculatorLake Louise score
Validated clinical scoring tool for acute mountain sickness. Five short questions, immediate score, with explanations of what each item means.
Roach et al. 2018.
Open calculatorBühlmann ZH-L16C
Sixteen-compartment dissolved gas model used by most modern dive computers. Predicts no-decompression limits and decompression stops for arbitrary dive profiles.
Bühlmann 1990. ZH-L16 algorithm.
Open calculatorCNS oxygen toxicity
NOAA CNS clock for oxygen partial pressures above 1.4 ATA. Predicts time to convulsion threshold during technical and saturation diving.
NOAA Diving Manual.
Open calculatorCardiovascular deconditioning
Modelled fall in cardiac mass and orthostatic tolerance over the duration of a microgravity mission, with and without exercise countermeasures.
Convertino et al. 1990s. Hargens and Richardson 2009.
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