Switch units, set precision, and convert wavenumbers to wavelengths fast with confidence. See frequency and photon energy, then export tables to share easily anywhere.
Wavenumber is the reciprocal of wavelength. Using consistent length units:
Here, c = 299,792,458 m/s and h = 6.62607015×10⁻³⁴ J·s.
| Wavenumber (cm⁻¹) | Wavelength (µm) | Frequency (THz) | Energy (eV) |
|---|---|---|---|
| 500 | 20.000 | 14.9896 | 0.0620 |
| 1000 | 10.000 | 29.9792 | 0.1240 |
| 2000 | 5.000 | 59.9585 | 0.2480 |
| 5000 | 2.000 | 149.8962 | 0.6199 |
| 10000 | 1.000 | 299.7925 | 1.2398 |
Spectroscopists report bands as wavenumber because it is proportional to energy and scales linearly with many vibrational transitions. Converting to wavelength helps when selecting optics, detectors, and laser sources. This calculator supports cm⁻¹, mm⁻¹, and m⁻¹ inputs for IR and metrology workflows. In FTIR, peaks near 1700 cm⁻¹ often indicate carbonyl stretching; 5.9 µm is easier to visualize in an optical layout.
Wavelength depends on the length unit. A handy shortcut is λ(µm)=10,000/ṽ(cm⁻¹). For example, 1000 cm⁻¹ corresponds to 10 µm, while 5000 cm⁻¹ corresponds to 2 µm. For visible light, 15,000–25,000 cm⁻¹ maps roughly to 667–400 nm. That corresponds to photon energies of roughly 1.86–3.10 eV.
Mid‑infrared features often appear from about 400 to 4000 cm⁻¹ (25 to 2.5 µm). Near‑infrared work commonly spans 4000 to 12,500 cm⁻¹ (2.5 to 0.8 µm). Raman shifts are reported in cm⁻¹ too, so converting can clarify filter and grating choices.
Inside a material, wavelength shortens by the refractive index n while frequency stays the same. The calculator reports both vacuum and medium wavelengths using λ_medium=λ_vacuum/n. For silica near 1550 nm, n is about 1.44, giving a medium wavelength near 1076 nm. For water, n near 1.33 shifts thin‑film interference.
Frequency provides an independent check: f=c/λ_vacuum. At 10 µm, f is about 29.98 THz; at 1 µm, f is about 299.79 THz. Photon energy follows E=hf, so 1 µm is about 1.24 eV, matching common photonics rules.
Reporting requirements differ across labs. Fixed decimals suit routine QC, while significant figures fit high‑dynamic‑range data. If your input uncertainty is 0.5 cm⁻¹, do not print eight meaningful digits for wavelength. Choose precision that reflects instrument resolution. When publishing, include the original wavenumber for reproducibility.
Two mistakes appear often: mixing vacuum and in‑medium wavelength, and forgetting the cm⁻¹ to m⁻¹ factor of 100. If a value is off by two orders of magnitude, check that conversion. A quick sanity test is λ(µm)=10,000/ṽ(cm⁻¹).
Downloadable CSV files work well for spreadsheets and instrument logs, while PDF summaries are convenient for attachments and QA binders. Exporting the same inputs and outputs reduces transcription errors and creates traceable records. Document units, refractive index assumption, and formatting mode very easily.
Wavenumber is the number of wave cycles per unit length, usually reported as cm⁻¹ in spectroscopy. It equals the reciprocal of wavelength when both use consistent length units.
Changing units rescales the numeric value. For example, 1 cm⁻¹ equals 100 m⁻¹. The calculator converts your input to m⁻¹ internally, then converts the final wavelength into your selected output unit.
No. Refractive index changes wavelength inside the medium, but frequency and photon energy remain set by the vacuum wavelength for the same radiation. The tool reports both vacuum and in‑medium wavelength for clarity.
For mid‑infrared bands, µm is often the most readable. For near‑infrared and visible, nm is common. Choose the unit that matches your instrument specifications, filter datasheets, or reporting standards.
Use λ(µm)=10,000/ṽ(cm⁻¹). If your calculator output in µm disagrees by about 100× or 0.01×, the most likely issue is a missing cm⁻¹ to m⁻¹ conversion factor.
Match precision to measurement uncertainty. If your spectrometer resolution is 1 cm⁻¹, reporting wavelength to six decimals usually overstates accuracy. Significant figures often communicate uncertainty more honestly across large ranges.
Exports reduce transcription errors and keep inputs, units, and assumptions together. CSV is ideal for spreadsheets and logs, while PDF is convenient for attachments, audit trails, and sharing consistent results with collaborators.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.