Shine a laser pointer through a narrow slit and the spot on the wall is not a clean dot — it spreads into a bright central band flanked by fading stripes. Light bends around obstacles, and the first dark stripe in a single slit obeys a crisp rule: the slit width times the sine of the angle equals the wavelength times the stripe number. In symbols: a sin θ = mλ. Wider slit, tighter pattern; longer wavelength, wider spread.

The CD on your shelf is a diffraction grating doing the same trick in reverse — its microscopic tracks split white light into the rainbow shimmer you see when you tilt it. Engineers use precision gratings to split starlight into spectra, identifying the elements in distant galaxies from the dark lines in their rainbows.

This calculator handles the path-difference product at the formula's heart. Type the slit (or grating) width in the Variable A box — in the same units as your wavelength — and the sine of the measured angle in the Variable B box. The Result box gives a sin θ, the path difference. Divide it by your light's wavelength λ to find m, the stripe number — whole numbers mark exactly where the dark fringes fall.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Diffraction Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.