Screw spacing calculator

Divides a run into equal gaps closest to your target spacing, and tells you how many fixings that needs. Fixings at both ends means one more fixing than there are gaps.

That off-by-one is the mistake this exists to prevent: a 2400 mm run at 300 mm spacing has eight gaps and nine fixings, not eight. Rounding to a whole number of gaps is the other half — you almost never want a short gap at one end, so the tool adjusts the spacing slightly to divide evenly rather than leaving a remainder. The difference figure tells you how far that adjustment took you from your target, which is what decides whether it is acceptable: a few millimetres on a fence rail is nothing, and the same few millimetres on visible cabinet work is not.