Cricket Chirp Thermometer - Dolbear's Law Temperature Estimate

A cricket chirp thermometer is a method of estimating air temperature by counting the chirps a cricket produces over a fixed time. The relationship between chirp rate and temperature, known as Dolbear's law, was first published in 1897 and has been refined for several common species such as the field cricket, snowy tree cricket, and common true katydid. The calculator on this page turns that counted rate into a temperature reading in degrees Fahrenheit or Celsius in real time.

• • Estimate outdoor temperature without a thermometer: Use it during a camping trip or backyard gathering when you do not have a digital thermometer handy.
• • Teach a science class about insect behavior: Bring a stopwatch to a schoolyard activity and let students plot their own chirp rate against a classroom thermometer.
• • Calibrate a backyard weather station: Cross-check the reading from a personal weather station against an insect-based estimate on still summer nights.
• • Practice field biology techniques: Use it as a low-cost exercise for citizen-science projects that track seasonal insect activity.

The classic version uses field crickets (Gryllus assimilis, G. integer, and related species) and works especially well between about 55 °F and 72 °F, where chirp rate changes in a nearly straight line with temperature. Below roughly 50 °F the field cricket typically stops singing, and the formula starts to extrapolate. If your local species behaves differently, count a few trials against a real thermometer and average the result before you trust the reading.

Because it requires no instrument beyond a watch, this approach is one of the most accessible citizen-science tricks in existence. It is also a useful example of how a single linear model can describe a biological process well enough to make a useful prediction.

For another quick field estimate that turns a small animal count into a useful number, see the Animal Mortality Rate Calculator, which uses USDA benchmark thresholds to spot unusual losses in a herd.

The calculator relies on a linear relationship between the rate at which a cricket calls and the surrounding air temperature. The form below is the version originally proposed by Amos Emerson Dolbear for the snowy tree cricket and later adapted for other common species.

• T_F: Estimated air temperature in degrees Fahrenheit at the cricket's location.
• chirps_per_minute: Average number of chirps in a 60-second window, scaled from your timed count.
• base, intercept, slope: Species-specific constants. Field cricket uses 50, 40, 4; snowy tree uses 50, 92, 4.7; common true katydid uses 60, 19, 3.

The chirps-per-minute value is computed by scaling your timed count to 60 seconds. If you counted 30 chirps in 30 seconds, the formula still uses 60 chirps/min, so the same temperature is reported. The calculator then picks the constants for the species you chose and returns an estimated air temperature in degrees Fahrenheit. A separate row in the result panel shows the Celsius equivalent, which is useful for field guides that quote either scale.

According to Wikipedia, Dolbear's 1897 equation T = 50 + (N - 40) / 4 was first reported for the snowy tree cricket, even though it is widely reused for the field cricket.

According to Scientific American, the underlying mechanism is the Arrhenius rate law, which is why cold-blooded insects such as crickets, katydids, and cicadas chirp at a rate that scales with ambient temperature.

If you are tracking a season of biology field work and want a similarly quick reference, the Cow Gestation Calculator maps a breeding date to a calving date with species-specific constants.

Four short ideas explain why a small insect can be turned into a thermometer, and why the readings are only approximate.

Each of these ideas matters for interpreting your reading. The Arrhenius link explains why a thermometer-style estimate is even possible; the species constants explain why the same chirp rate in two locations can imply different temperatures.

Students who want a classroom companion to the chirp-rate model can use the Allele Frequency Calculator to practice population-level biology calculations in the same Education & Academic category.

Count carefully once, then let the calculator do the math.

1. 1 Pick the species you are listening to: Field cricket is the default. Switch to snowy tree cricket if the song comes from shrubs and trees, or common true katydid if the calls come from the canopy at dusk.
2. 2 Grab a watch or phone timer: Use a stopwatch you can read at a glance, and decide on a counting window before you start so you are not switching between two tasks mid-count.
3. 3 Count chirps from a single cricket: Cricket choruses overcount. Move a few meters away from other singers if you can, and avoid windy nights where wind noise can mask chirps.
4. 4 Type the count and the time: Enter the number of chirps you heard and the number of seconds you spent counting. The default 60 s works for the classic Dolbear method.
5. 5 Read the temperature in °F and °C: The result panel shows the estimated temperature, the Celsius equivalent, and the chirps-per-minute value that drove the calculation.
6. 6 Repeat and average three trials: Count a second and third time on the same cricket, average the three chirp rates, and rerun the calculator for a more stable estimate.

Practical example: standing in the backyard at 9 p.m., you count 60 chirps in 60 seconds from a single field cricket in the grass. After typing 60 chirps, 60 seconds, and field cricket, the calculator returns 55 °F, which lines up with the digital thermometer on your porch.

When you are ready to switch from outdoor biology to lab biology, the Annealing Temperature Calculator helps pick a primer temperature using a similar species- and machine-specific constants approach.

This low-cost, low-tech method is a useful way to estimate temperature. Use it when other tools are not available, or as a teaching aid.

• • No instrument required: All you need is your ears, a watch, and a clear night. It works on a camping trip, a school field trip, or in your own backyard.
• • Quick, real-time result: The calculator shows the temperature in both Fahrenheit and Celsius the moment you finish counting, so you can plan a jacket or a sleeping bag without waiting for a weather report.
• • Educational value: It is a ready-made classroom demonstration of how a simple linear model can describe a biological process, which is a useful talking point for biology and physics lessons.
• • Citizen-science friendly: A single timed count is enough to contribute to local phenology projects that track when insects begin singing in spring and stop in fall.
• • Cross-check for digital sensors: Use the reading to spot-check a home weather station that may be wrong on a still, sheltered night where wind-driven cooling is not the dominant effect.

The reading is a quick estimate, not a substitute for a calibrated instrument. Treat it as a sanity check on the air around you rather than a precise measurement.

A cricket-based estimate works only if you keep a few variables in mind. Each factor below changes how much you should trust the result.

• • The formula is a linear approximation. It works best in the 55–72 °F range and is only a rough guide outside that window.
• • Different populations of the same species chirp at slightly different rates. Calibrate the result against a real thermometer once a season for the most accurate reading.
• • A chorus inflates the count, so single-cricket readings are more accurate than busy field-edge counts.

Treat the result as a quick, approximate reading. The calculator returns the value the linear model predicts, but the actual air temperature can vary by a few degrees depending on the species, the night, and how carefully you counted.

According to Wikipedia, the original Dolbear shortcut is to count the number of chirps in a short window and add 40 to obtain a quick estimate of the air temperature in degrees Fahrenheit. NOAA NWS field guides and the calculator's default counting time (60 seconds) both apply the same underlying linear model.

For a different take on a date-of-event prediction grounded in biology, the Cat Pregnancy Calculator estimates a feline due date from a breeding record and a species-specific gestation length.