What is redshift in astronomy?

The stretching of light wavelengths toward red, caused by an object moving away or by the expansion of space.

How is redshift (z) calculated?

z = (observed wavelength − emitted wavelength) ÷ emitted wavelength.

Why is redshift key evidence for the expanding universe?

More distant galaxies show greater redshift proportional to distance, matching cosmic expansion predictions.

Redshift Calculator - CalculatorLabs.net

Redshift Calculator

Observed Wavelength (nm)

Emitted (Rest) Wavelength (nm)

Instant Result

Redshift (z) -

Recession Velocity -

What Is a Redshift Calculator?

Redshift measures how much a distant object's light has been stretched to longer (redder) wavelengths, usually because the object is moving away from us — a cornerstone piece of evidence for the expanding universe. This calculator finds the redshift z and the approximate recession velocity (valid for z well below 1).

How to Use This Redshift Calculator

Enter the observed wavelength of a spectral line, in nanometers.
Enter the wavelength that same spectral line has at rest (in a lab), in nanometers.
Click Calculate to get the redshift z and the approximate recession velocity.

Formula

z = (λ_observed − λ_emitted) / λ_emitted
v ≈ c × z (valid for z << 1)

Worked Example

A spectral line at rest is 500 nm, observed at 500.5 nm. z = (500.5 − 500)/500 = 0.001. Recession Velocity ≈ 299,792.458 × 0.001 ≈ 300 km/s.