A cricket is a thermometer with legs. Because crickets are cold-blooded, the chemistry of their chirping muscles speeds up and slows down with the air temperature — warm evenings produce fast chirps, cool evenings produce lazy ones. In 1897 the physicist Amos Dolbear turned that relationship into a formula famous enough to carry his name. This crickets chirping thermometer applies Dolbear’s law for you: count the chirps, pick your counting method, and read the temperature in Fahrenheit and Celsius.
How to Use the Crickets Chirping Thermometer
Pick one cricket — ideally the loudest, closest singer — and time it. For the classic field-cricket method, count its chirps in 14 seconds and add 40 to get the temperature in Fahrenheit. For the snowy tree cricket, famous as the most accurate natural thermometer, count for 13 seconds and add 40. If you prefer a full minute, use Dolbear's original published form. Enter your count, choose the matching method above, and the calculator returns both Fahrenheit and Celsius.
Dolbear's Law: The Formula Behind the Chirps
Amos Dolbear published the relationship in 1897 as T = 50 + (N − 40) ÷ 4, where T is the temperature in Fahrenheit and N is chirps per minute. A cricket chirping 120 times a minute gives T = 50 + 80 ÷ 4 = 70 °F. The simplified counting rules come straight from that equation: in 14 seconds a field cricket chirps roughly one quarter of its per-minute count, and the arithmetic collapses to the memorable "count for 14 seconds and add 40." The law works because chirping is powered by muscle contractions, and muscle reaction rates climb steadily with temperature in a cold-blooded animal.
Worked Example: A Summer Evening
You count a field cricket at 30 chirps in 14 seconds. Adding 40 gives 70 °F, which is 21.1 °C — a mild evening, exactly matching the feel of the night. Cross-check with the per-minute form: 30 chirps in 14 seconds scales to about 129 chirps a minute, and Dolbear's original formula gives 50 + (129 − 40) ÷ 4 = 72.3 °F. The two methods landing within about two degrees of each other is typical — treat the result as a good estimate, not a laboratory reading.
Which Cricket Should You Count?
The snowy tree cricket is the gold standard: its chirp rate tracks temperature so faithfully that naturalists call it the thermometer cricket, and groups of them synchronize so a whole tree sings at one tempo. Field crickets are the next best and are the species behind the 14-second rule. Ground crickets and katydids follow the same principle with different constants, so if your singer is not one of the two species in the calculator, expect a few degrees of error. Whatever the species, count one individual — a chorus of overlapping chirps inflates the count.
Why It Works: Cold Blood and Fast Chemistry
Crickets do not regulate their body temperature, so their internal temperature is the air temperature. Every step in producing a chirp — nerve signals, muscle contraction, wing movement — is a chemical process, and chemical reaction rates roughly double with each 10 °C rise. The chirp rate therefore becomes a readable dial of the surrounding temperature. This is also why the method fails below about 50 °F: the chemistry slows so much that most crickets simply stop singing.
Tips for an Accurate Reading
Count for the full timed window with a phone stopwatch rather than estimating. Repeat the count two or three times and average. Stay close to one cricket and ignore distant singers. Take the reading at cricket height — in grass or low shrubs — since air near the ground can be several degrees cooler than at head height on still nights. And remember the method reports the temperature where the cricket sits, in shade, which is the honest outdoor temperature anyway.
A Note on Folklore Versus Physics
The cricket method sits in a rare category: a piece of folk wisdom that survived laboratory testing. Naturalists repeated Dolbear's counts across species and regions through the twentieth century and kept confirming the linear relationship, with each species simply owning a different intercept. That is why the calculator insists on matching the counting method to the species — the physics is universal, but the constants belong to the cricket. Treat the result as the temperature of the grass at dusk, measured by its most reliable resident.
Related Tools
Find more nature and lab tools in the Biology Calculators hub, including the Generation Time Calculator for growth rates and the Basal Area Calculator for forestry work.
Frequently Asked Questions
How accurate is the cricket thermometer?
With a snowy tree cricket and careful counting, usually within 1 to 2 °F of a real thermometer. With field crickets, within a few degrees. It is an estimate good enough for deciding on a jacket, not for calibrating equipment.
What is the 14-second cricket rule?
Count a field cricket's chirps in 14 seconds and add 40 — the result is the temperature in Fahrenheit. It is the simplified form of Dolbear's law, published in 1897.
How do I convert the cricket temperature to Celsius?
Subtract 32 from the Fahrenheit result and multiply by 5/9. The calculator shows both units automatically — 70 °F, for example, is 21.1 °C.
Do all crickets chirp at the same rate for a given temperature?
No. Each species has its own rate-to-temperature relationship. The snowy tree cricket and field cricket have well-established constants, which are the two the calculator uses; other species need their own calibration.
Why do crickets stop chirping when it gets cold?
Their muscles are powered by temperature-dependent chemistry. Below roughly 50 °F the reactions run too slowly to sustain chirping, so the insects fall silent — silence itself is a rough cold signal.
Can I use chirps per minute instead of a timed count?
Yes — choose the Dolbear original method and enter chirps counted over 60 seconds. The formula is T = 50 + (N − 40) ÷ 4 in Fahrenheit.
Does the cricket method work during the day?
It works whenever crickets sing, but most chirping species are evening and night singers, and direct sun heats surfaces unevenly, so dusk readings in shade are the most reliable.