What this calculator does
Crickets chirp faster when it is warmer, closely enough that the relationship can be used as a thermometer. Amos Dolbear published the observation in 1897, and the field cricket version is 50 plus the chirps per minute less 40, divided by 4, giving degrees Fahrenheit.
The species matters a great deal. The snowy tree cricket is the one Dolbear law was originally fitted to and is the most reliable, while field crickets and katydids need their own constants. Applying the field cricket formula to a katydid at 80 chirps a minute gives 60°F against the katydid formula 80°F, a difference of more than 11 Celsius degrees.
The formula
Each species has its own linear formula relating chirps per minute to temperature in Fahrenheit, and the result is converted to Celsius alongside. The field cricket uses 50 plus (N − 40) divided by 4, the snowy tree cricket 50 plus (N − 92) divided by 4.7, and the katydid 60 plus (N − 19) divided by 3.
| Term | Meaning |
|---|---|
| Dolbear law | The 1897 relationship between cricket chirp rate and air temperature. |
| Chirps per minute | The count of chirps, which for the snowy tree cricket is conventionally taken as chirps in 13 seconds plus 40. |
| Snowy tree cricket | The species the original law was fitted to, and the most reliable natural thermometer of the three. |
The inputs explained
| Field | What to enter |
|---|---|
| Species | The cricket species, which changes the formula substantially. Identifying the species correctly matters more than counting precisely. |
| Chirps counted per minute | Chirps counted per minute. Counting for 15 seconds and multiplying by four is the practical approach. |
When to use it
Estimating temperature without a thermometer
A genuinely usable field method within the species normal temperature range, and accurate to within a couple of degrees for the snowy tree cricket.
Demonstrating a linear relationship
It is a common teaching example precisely because the relationship is close to linear, easy to test outdoors and gives an answer that can be checked against a real thermometer.
Checking which species you are hearing
Running the count through each formula and comparing against a known temperature identifies which species fits, which is a reverse use of the same relationship.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What temperature does each chirp rate indicate?
A range of chirp rates using the field cricket relationship.
| Chirps per minute | Temperature (°F) | Temperature (°C) | Chirps per minute used |
|---|---|---|---|
| 60 | 55.0 °F | 12.8 °C | 60 |
| 80 | 60.0 °F | 15.6 °C | 80 |
| 100 | 65.0 °F | 18.3 °C | 100 |
| 120 | 70.0 °F | 21.1 °C | 120 |
How much does species identification matter?
The same chirp count interpreted under each of the three species formulas.
| Species | Temperature (°F) | Temperature (°C) | Species formula used |
|---|---|---|---|
| Field cricket | 60.0 °F | 15.6 °C | Field cricket: 50+(N−40)/4 |
| Snowy tree cricket | 47.4 °F | 8.6 °C | Snowy tree cricket: 50+(N−92)/4.7 |
| Common true katydid | 80.3 °F | 26.9 °C | Katydid: 60+(N−19)/3 |
Questions
How accurate is the cricket thermometer?
For the snowy tree cricket, generally within a degree or two Fahrenheit across its normal range, which is remarkably good for a method requiring no equipment. Field crickets are less consistent, and accuracy falls at temperature extremes where the insects chirp irregularly or stop.
How do I count chirps accurately?
Count for 15 seconds and multiply by four. The traditional snowy tree cricket shortcut is to count chirps in 13 seconds and add 40, which gives the temperature in Fahrenheit directly and is equivalent to the full formula.
Why do crickets chirp faster when it is warm?
Because they are ectothermic, so their muscle chemistry runs at the speed the ambient temperature permits. The chirp is produced by rubbing the wings together, and the rate of that movement is limited by reaction rates that rise with temperature, which is the same Q10 effect that governs biological rates generally.
Does it work in cold weather?
Poorly, and eventually not at all. Below about 55°F most species chirp slowly and irregularly, and below roughly 50°F they largely stop. The method only works in the range where the insects are active enough to produce a steady, countable rate.
For the general temperature dependence of biological rates, see the Q10 coefficient calculator. For heat accumulation in crops, see the growing degree days calculator.