About the Cricket Thermometer

The Cricket Thermometer is a free web app that uses your phone or computer's microphone to listen to crickets and calculate the air temperature from how fast they chirp. It is based on Dolbear's Law, a scientific formula published by physicist Amos Dolbear in 1897 that describes how a cricket's chirp rate increases with temperature.

Supported species include the snowy tree cricket (Oecanthus fultoni), field crickets (Gryllus species), and the common true katydid (Pterophylla camellifolia). The app provides readings in both Celsius and Fahrenheit, includes a live spectrum analyser, and shows a confidence rating for each reading.

The Cricket Thermometer is a Progressive Web App (PWA) that works offline once installed on your home screen. It is free, contains no advertising, and stores all data on your device.

LIVE FIELD INSTRUMENT

Cricket
Thermometer

a real working science experiment

—°C
no reading yet
Press the button below and let the crickets sing!
SOUND • cricket band 3–5 kHz
14″

📊 Live data

Chirps detected0
Chirps per minute—
Peak frequency—
Signal strength—
Reading confidenceawaiting data

Which cricket are you listening to?

Different species chirp at different rates. Choose the closest match.

Photo credits: Snowy tree cricket by photographer name · CC BY-NC 4.0 Field cricket by photographer name · CC BY-NC 4.0 Common true katydid by photographer name · CC BY-NC 4.0

How does this actually work?

The 1897 cricket formula

In 1897, an American physicist named Amos Dolbear noticed that crickets chirp faster when it's warm and slower when it's cold. So he wrote down a formula:

T(°F) = 50 + (N − 40) ÷ 4 where N = the number of chirps in one whole minute.

For Celsius, the formula becomes:

T(°C) = 10 + (N − 40) ÷ 7.2 same N — just converted.

There's a quick version too: count the chirps in 14 seconds, then add 40. That gives you the temperature in Fahrenheit. (We don't make you do the maths — the app counts for you!)

What is the app actually listening for?

Crickets sing in a narrow range of high pitches — about 3,000 to 5,000 Hertz. That's higher than a human voice but lower than a smoke alarm.

The app uses your phone's microphone to listen. It splits the sound into frequencies (using something called a Fast Fourier Transform) and only pays attention to the cricket band. When it sees a sharp spike of energy in that band, it counts it as one chirp.

It also checks that the spike is coming just from the cricket band, not all over the spectrum. That way, things like talking or wind don't get counted by mistake.

How to get the best reading
  1. Go outside on a warm summer evening after sunset.
  2. Stand quietly near where you can hear chirping clearly.
  3. Hold your phone with the microphone facing the crickets.
  4. Try not to move or make noise during the 14 seconds.
  5. If you can hear several different cricket species, pick a quieter spot — the app counts best when one species is clearest.
  6. If the chirp count seems too low, try recording again. Crickets sometimes pause.
Why isn't it always perfectly accurate?

Dolbear's formula was made for one specific species: the snowy tree cricket. Other crickets don't follow the formula as exactly.

Also, real-world things mess with the reading:

• Wind makes broadband noise that masks the chirps.
• Distance — chirps get quieter and harder to detect.
• Other crickets — if two species chirp at different speeds, the count gets mixed up.
• Cold nights — below about 13°C / 55°F, crickets often stop chirping altogether.

If the confidence reading is low, the temperature number is just a rough guide.

Install this on your phone

This is a Progressive Web App — once installed, it works without internet, which is helpful if you're in a field somewhere.

iPhone: tap the Share button → "Add to Home Screen".
Android: tap the menu (three dots) → "Install app" or "Add to Home screen".