What is the speed of sound?
343 m/s in dry air at 20°C. It increases with temperature and is faster in liquids and solids.
Wave Speed Calculator
v = fλ
Calculate wave speed from frequency and wavelength. v = fλ — applies to all waves: sound, light, water.
Calculate
Enter values above to calculate
How it calculates
1
v = f × λ
2
f in Hz (s⁻¹), λ in metres
3
Result in m/s
Formula
v = fλ
Variable Table
| Symbol | Quantity | SI Unit |
|---|---|---|
| v | Wave speed | m/s |
| f | Frequency | Hz |
| λ | Wavelength | m |
| T | Period = 1/f | s |
How to Use This Calculator
This wave speed calculator is built for quick physics checks and worked-problem review. Enter values in the units shown beside each input, then compare the result with the formula and variable table before using it in a longer solution. The calculator does the arithmetic, but the physics still depends on choosing a model that matches the situation.
Start by identifying the system, the known quantities, and the quantity you want to find. If a value is given in a non-SI unit, convert it before substitution. A correct numerical answer with mixed units can still be physically wrong, especially when squared units, inverse seconds, charges, temperatures, or distances are involved.
Assumptions and Limits
The formula v = fλ is a model, not a universal description of every possible case. It assumes the quantities in the variable table are the relevant quantities for the problem and that hidden effects are either negligible or already included in the inputs. If friction, drag, relativistic speeds, changing fields, non-constant temperature, or geometry-specific effects matter, check whether a more complete model is needed.
Use the result as a magnitude and units check. Ask whether the answer has the right sign, whether it grows or shrinks when an input changes, and whether the limiting cases make sense. Setting an input to zero, doubling a quantity, or using a very large value is often enough to catch a formula choice or unit mistake before it reaches a final answer.
Worked Example
Sound wave: f = 440 Hz, λ = 0.78 m. Find wave speed.
Step 1: v = f × λ
Step 2: v = 440 × 0.78
Answer: v ≈ 343 m/s (speed of sound in air at 20°C ✓)
Common Mistakes
- Frequency does not change between media — speed and wavelength do
- v = c/n for light in a medium
- Convert nm to m for light wavelengths (1 nm = 10⁻⁹ m)
Related
Frequently Asked Questions
What is the speed of light?
c = 299,792,458 m/s in vacuum (exact, by definition). In glass, it slows to ≈ c/1.5.