Speed of Sound Calculator
The speed of sound in air at a given temperature, in every common unit, and the time sound takes to cover a distance — the lightning-and-thunder count made exact.
Sound travels through air at a speed set by temperature alone (pressure and altitude barely matter, humidity a little): c = 331.
How the speed of sound calculator works
Sound travels through air at a speed set by temperature alone (pressure and altitude barely matter, humidity a little): c = 331.3 × √(1 + T ÷ 273.15) m/s, about 343 m/s at 20 °C and 0.6 m/s faster for every degree. Divide a distance by that speed for the delay — roughly three seconds per kilometer, five per mile.
Formula: c = 331.3 × √(1 + T ÷ 273.15); t = d ÷ c
Worked examples
| Inputs | Speed of sound (m/s) | Note |
|---|---|---|
| 20 °C | 343.2 | 343.2 m/s |
| A freezing day, 0 °C | 331.3 | 331.3 m/s |
| A hot day, 40 °C | 354.7 | 354.9 m/s |
FAQFrequently asked questions
How far away is the lightning?
Count the seconds between the flash and the thunder and divide by three for kilometers (by five for miles). Light arrives essentially instantly; sound takes about 2.9 seconds per kilometer.
Does altitude or pressure change the speed of sound?
Not directly — for an ideal gas the speed depends on temperature and the gas, not the pressure. Altitude matters only because it is colder up there, which is why the speed of sound drops with height in the atmosphere.
What about humidity?
Moist air is very slightly faster — water vapour is lighter than the air it displaces — by about 0.1–0.6% at ordinary temperatures. The formula here is for dry air.
How fast is sound in water or steel?
Much faster: about 1,480 m/s in fresh water, 1,530 in seawater and around 5,900 m/s in steel, because those media are far stiffer relative to their density.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Institute of Standards and Technology — the US measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.