Diffraction Grating Calculator
Calculate an ideal principal-maximum angle, grating spacing and highest possible order.
What would you like to do next?
Locate an ideal grating maximum at normal incidence
Enter grating density in lines per millimeter, a nonnegative integer diffraction order and wavelength in nanometers. The calculator converts line density into spacing, solves the normal-incidence grating equation and reports the highest possible nonnegative order. This makes impossible order-and-wavelength combinations visible instead of forcing an invalid inverse sine.
Separate the geometric angle from instrument response
A real spectrometer also depends on incidence angle, blaze geometry, illuminated width, slit width, detector position and wavelength-dependent efficiency. Misalignment and finite resolution broaden measured peaks. Use calibrated equipment geometry when identifying spectral lines or setting a detector, and keep units consistent before comparing the ideal result with an observation.
Frequently asked questions
Must diffraction order be an integer?
Yes. Principal maxima are labeled by integer orders.
What makes an order impossible?
The required sine exceeds one when order times wavelength is larger than grating spacing.
Does the tool include grating blaze efficiency?
No. It calculates ideal maximum geometry only.