Wavelength to wavenumber converter
Enter a value in either field. The values are inversely related.
Standard formula: Wavenumber = 107 / Wavelength (nm).
Enter a value to calculate.
How it works?
Wavelength (\(\lambda\)) represents the distance between wave peaks. Wavenumber (\(\tilde{\nu}\)) is the inverse: the number of waves that fit into a set distance (usually 1 centimeter).
Where:
- \(\tilde{\nu}\) : Wavenumber (cm⁻¹). Standard for IR Spectroscopy.
- \(\lambda\) : Wavelength (nm). Standard for UV-Vis/Telecom.
- 10^7 : Unit conversion factor (nm to cm).
Note: High energy = Short wavelength = High wavenumber. (e.g., 1000 nm = 10,000 cm⁻¹).
Why use Wavenumbers instead of Wavelength?
In the world of optics, you usually think in terms of Wavelength (nm)—the physical distance between two wave peaks. However, in spectroscopy and quantum mechanics, Wavenumber (cm⁻¹) is the preferred unit. Why? Because Wavenumber is directly proportional to Energy, making it far more intuitive when analyzing molecular vibrations and atomic transitions.
Spectroscopy Reference Table
Common spectral regions and their values in both units.
| Spectral Region | Wavelength (nm) | Wavenumber (cm⁻¹) |
|---|---|---|
| Deep UV (Excimer) | 193 nm | 51,813 cm⁻¹ |
| Violet / Blue | 400 nm | 25,000 cm⁻¹ |
| Green (Nd:YAG) | 532 nm | 18,797 cm⁻¹ |
| Red (HeNe) | 632.8 nm | 15,803 cm⁻¹ |
| Near Infrared (Telecom) | 1550 nm | 6,452 cm⁻¹ |
| Mid-IR (C-H Stretch) | 3,333 nm | 3,000 cm⁻¹ |
| Thermal IR | 10,000 nm (10 µm) | 1,000 cm⁻¹ |
| Far Infrared | 50,000 nm (50 µm) | 200 cm⁻¹ |
Why this conversion is indispensable
1. Proportional to Energy
Wavelength (λ) is inversely proportional to energy (E = hc/λ). This is confusing: a bigger number (long wavelength) means less energy. Wavenumber (ṽ) fixes this—a bigger number means more energy, making spectrum interpretation intuitive.
2. Raman Spectroscopy
Raman shifts are always reported in cm⁻¹. This allows scientists to compare vibrational modes (e.g., a benzene ring stretch at 992 cm⁻¹) regardless of whether they use a green (532 nm) or infrared (785 nm) excitation laser.
3. Infrared (FTIR) Fingerprinting
Chemical bonds vibrate at specific frequencies. The carbonyl group (C=O) always absorbs around 1700 cm⁻¹. Using wavenumbers creates a universal "fingerprint" map for identifying chemical compounds.
4. Laser Physics
When calculating the energy difference between two laser states, subtracting wavelengths gives the wrong answer. You must convert to wavenumbers (or frequency) first to accurately calculate the transition energy gap.
Related Engineering Tools
Convert Wavelength to Frequency (THz). Frequency is the "time-based" cousin of Wavenumber.
Photon EnergyCalculate the exact energy (eV or Joules) carried by a specific wavenumber.
Angstrom to NanometerSwitch between length scales when dealing with crystallography and atomic bonds.