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Instant conversion between 11 spectroscopic units — wavenumber, wavelength, frequency, and energy
| cm⁻¹ | nm | μm | THz | eV | Assignment |
|---|---|---|---|---|---|
| 3,400 | 2,941 | 2.94 | 101.9 | 0.4214 | O-H stretch |
| 2,950 | 3,390 | 3.39 | 88.4 | 0.3657 | C-H stretch |
| 1,720 | 5,814 | 5.81 | 51.6 | 0.2132 | C=O stretch |
| 1,650 | 6,061 | 6.06 | 49.5 | 0.2045 | Amide I / C=C |
| 1,550 | 6,452 | 6.45 | 46.5 | 0.1921 | Amide II |
| 1,040 | 9,615 | 9.62 | 31.2 | 0.1289 | C-O stretch |
| 1,000 | 10,000 | 10.0 | 30.0 | 0.1240 | Fingerprint region |
| 720 | 13,889 | 13.9 | 21.6 | 0.0893 | C-H rock (long chain) |
| 500 | 20,000 | 20.0 | 15.0 | 0.0620 | Metal-O stretch |
| 200 | 50,000 | 50.0 | 6.0 | 0.0248 | Lattice vibration |
Values calculated using NIST 2018 CODATA recommended constants. Click any preset above to load a value into the converter.
Spectroscopists routinely switch between wavenumber, wavelength, frequency, and energy representations depending on the technique, the journal, or the audience. Getting the conversion right matters — especially when comparing results across UV-Vis, IR, and Raman measurements that each favor different units.
The SpectralBench unit converter handles all common spectroscopic units in one place. Enter a value in any field and every other unit updates instantly. Calculations use NIST-recommended physical constants so you can trust the results in publications and reports. Need to convert peak positions from an FTIR measurement? Load your spectrum in the Spectral File Viewer and use the converter alongside it. You can also browse spectra in different units using the reference library.
Enter a value in any of the eleven unit fields — wavenumber (cm⁻¹), wavelength (nm, μm), frequency (Hz, THz, GHz), energy (eV, meV, J, kJ/mol, kcal/mol). All other fields update in real time with the converted values. The conversion is bidirectional: change any field and the rest recalculate instantly.
SpectralBench uses NIST 2018 CODATA recommended values for physical constants including the speed of light, Planck's constant, and the elementary charge. This ensures your converted values are accurate enough for publication-quality work and consistent with international measurement standards.
The wavenumber to wavelength conversion uses the reciprocal relationship derived from the definition ν̃ = 1/λ. The conversion factor depends on the wavelength unit:
λ(nm) = 10⁷ / ν̃(cm⁻¹)
λ(μm) = 10⁴ / ν̃(cm⁻¹)
For example, 1000 cm⁻¹ = 10,000 nm = 10 μm, and 3000 cm⁻¹ = 3,333 nm = 3.33 μm (the C-H stretch region).
The wavelength to wavenumber conversion is the inverse of the above:
ν̃(cm⁻¹) = 10⁷ / λ(nm)
ν̃(cm⁻¹) = 10⁴ / λ(μm)
Converting 550 nm (green visible light) gives 18,182 cm⁻¹. Converting 2.5 μm (start of mid-IR) gives 4,000 cm⁻¹. Remember: higher wavenumber = shorter wavelength = higher energy.
Frequency and wavenumber are directly proportional through the speed of light:
f(Hz) = ν̃(cm⁻¹) × c, where c = 2.998 × 10¹⁰ cm/s
f(THz) = ν̃(cm⁻¹) × 0.02998
The conversion factor 1 THz ≈ 33.36 cm⁻¹ is useful for far-IR and THz spectroscopy. For example, 1000 cm⁻¹ = 29.98 THz.
Wavenumber is directly proportional to photon energy through the fundamental equation E = hcν̃:
E(eV) = ν̃(cm⁻¹) × 1.2398 × 10⁻⁴
E(kJ/mol) = ν̃(cm⁻¹) × 0.01196
The mid-IR range (400–4000 cm⁻¹) corresponds to 0.05–0.50 eV, while the UV-Vis range (12,500–50,000 cm⁻¹) spans 1.5–6.2 eV. All conversions use NIST 2018 CODATA recommended values for physical constants.
Want to understand WHY spectroscopists use wavenumber? Read our guide →
Enter a wavenumber value in cm⁻¹ into SpectralBench and the wavelength in nanometers updates instantly. The formula is λ(nm) = 10⁷ / ν̃(cm⁻¹). For example, 1000 cm⁻¹ equals 10,000 nm (10 μm).
Wavenumber (cm⁻¹) and wavelength (nm) are reciprocally related: a higher wavenumber corresponds to a shorter wavelength and higher energy. The conversion is λ(nm) = 10⁷ / ν̃(cm⁻¹). This inverse relationship means equal steps in wavenumber do not correspond to equal steps in wavelength.
Wavenumber is directly proportional to energy and frequency, making it the natural unit for infrared and Raman spectroscopy. Equal spacing in wavenumber corresponds to equal spacing in energy, which simplifies spectral interpretation, peak comparison, and thermodynamic calculations.
1000 cm⁻¹ equals 10,000 nm, which is 10 μm. This falls in the mid-infrared region of the electromagnetic spectrum, where many molecular vibrations (C-O, C-N, and fingerprint region absorptions) are observed.
To convert THz to wavenumber, use the formula ν̃(cm⁻¹) = f(THz) × 10¹² / (c × 100), where c = 2.998 × 10⁸ m/s. In practice, 1 THz ≈ 33.36 cm⁻¹. Enter your THz value in SpectralBench and the wavenumber updates instantly alongside all other units.
3000 cm⁻¹ equals 3,333 nm (3.33 μm). This region is important in infrared spectroscopy as it contains C-H stretching vibrations — one of the most commonly identified absorption bands in organic chemistry.
Use the formula ν̃(cm⁻¹) = E(eV) / (1.2398 × 10⁻⁴). For example, 1 eV corresponds to approximately 8,066 cm⁻¹. SpectralBench handles this conversion automatically — enter any eV value and see the wavenumber result instantly.
Visible light spans approximately 12,820 to 25,000 cm⁻¹, corresponding to wavelengths of 400–780 nm. Red light (~633 nm) is about 15,800 cm⁻¹, while violet light (~400 nm) is about 25,000 cm⁻¹. The SpectralBench converter shows the EM spectrum position for any value you enter.
To convert nanometers to micrometers, divide by 1000: λ(μm) = λ(nm) / 1000. For example, 2500 nm = 2.5 μm. This is useful when switching between near-IR (often reported in nm) and mid-IR (typically in μm or cm⁻¹) spectroscopy conventions.
SpectralBench converts between 11 spectroscopic units: wavenumber (cm⁻¹), wavelength (nm, μm), frequency (Hz, THz, GHz), and energy (eV, meV, J, kJ/mol, kcal/mol). All conversions use NIST 2018 CODATA recommended values for physical constants.
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