Free tool · Poultry
Poultry Heat Stress (THI) Calculator
Enter the temperature and humidity in your shed to get the Temperature-Humidity Index — the real heat your birds feel — and whether you are in the comfort, alert, danger or emergency zone.
Act immediately — heat loss is likely without aggressive cooling.
| THI | Zone | What it means |
|---|---|---|
| < 74 | Normal | Comfort |
| 74 – 78 | Alert | Ventilate, watch for panting |
| 79 – 83 | Danger | Cool actively now |
| ≥ 84 | Emergency | Aggressive cooling, losses likely |
THI combines temperature and humidity into the heat birds actually feel. Thresholds are general livestock guidance; younger birds and poor airflow shift the real risk earlier.
Why temperature alone lies to you in summer
On a humid afternoon, birds cannot shed heat by panting, so 35 °C at 70% humidity is far more dangerous than 35 °C in dry air. THI captures that by folding temperature and humidity into one number. In a closed shed, crossing into the danger zone can turn into mortality within the hour — so the value of THI is the warning it gives you while there is still time to fog, ramp fans and cool the birds.
From a one-off reading to a live alarm
A calculator tells you the THI right now. The losses happen when nobody is checking — a fan stalls, the afternoon spikes, and the shed crosses into danger unnoticed. Continuous monitoring watches THI around the clock and calls your phone the moment it climbs. See how that works on the poultry farm monitoring page, and use our broiler FCR calculator to see what heat stress costs you in feed.
FAQ
Poultry heat stress (THI) — common questions
What is THI in poultry?
THI (Temperature-Humidity Index) combines air temperature and relative humidity into one number that reflects the heat birds actually feel. High humidity stops birds from cooling themselves by panting, so the same temperature is far more dangerous in muggy weather — which is why temperature alone understates heat-stress risk.
How is THI calculated?
This tool uses the standard livestock formula with temperature in °C and humidity in %: THI = (1.8 × T + 32) − (0.55 − 0.0055 × RH) × (1.8 × T − 26). The result maps to comfort, alert, danger and emergency zones.
What THI is dangerous for chickens?
As general guidance, below 74 is the comfort zone, 74–78 is alert (ventilate and watch for panting), 79–83 is danger (cool actively), and 84 or above is an emergency. Younger birds and poor airflow shift the real risk earlier, so treat the bands as a warning, not a hard line.
How do I reduce heat stress when THI is high?
Increase airflow, run foggers or evaporative cooling, ensure cool clean water, avoid handling birds in peak heat, and adjust feeding times. The key is acting before birds start gasping — which means knowing the THI is climbing in time, ideally via continuous monitoring with an alarm.