Diffraction Grating Calculator
This calculator works out where a diffraction grating sends light, using the standard diffraction equation d sin(theta) = m lambda. It suits physics students and anyone checking spectroscopy or interference calculations who needs the diffraction angle, grating spacing, or maximum usable order for a given grating and wavelength. Enter the grating's line density in lines per millimetre, the wavelength of light in nanometres (or pick a preset such as sodium D-line, green laser, or red HeNe laser), and the diffraction order you want to check, from the central maximum (m = 0) upward. The calculator converts your line density into grating spacing automatically, then returns the diffraction angle for that order, sin(theta), and the highest order the grating and wavelength combination can physically produce before sine would need to exceed 1. It also lists the angle and visibility of every order up to that maximum in a table, so you can see the full fringe pattern at a glance, plus a plain-language summary of whether your chosen order is achievable. Use it to plan or check practical spectroscopy work, verify NCEA or university physics problems on gratings and interference, or see how changing line density or wavelength shifts the fringe pattern. The results assume normal incidence and an ideal transmission grating, so treat them as a guide for coursework rather than a substitute for your own working.
1. Grating and Light
2. Diffraction Order
The calculator also shows the highest order this grating and wavelength combination can physically produce, and the diffraction angle for every valid order up to that maximum.
Diffraction Angles by Order
| Order (m) | sin(theta) | Angle (theta) | Status |
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