What this calculator spaces
I use this sort of calculation for slats, fence pickets, wall battens, coat hooks, drawer pulls, dowels and rows of holes. The calculator assumes every item has the same width, the first and last items have matching margins from the ends, and every clear gap between neighbouring items is equal.
If you are marking drill centres or hooks rather than fitting something with a physical width, enter zero for the item width. The result then becomes a straightforward set of equally spaced point positions.
How to mark the positions
Measure every centre position from the same end of the workpiece. Do not repeatedly add the centre spacing with a ruler if accuracy matters, because small marking errors can accumulate. The complete list gives you one reference measurement for every mark.
Item width matters because equal centres and equal clear gaps are not the same thing. Once the items have width, the centre spacing is the clear gap plus one item width.
How to calculate equal spacing between items
First remove both end margins and the combined width of all the items from the total span. Divide what remains by one fewer than the number of items:(span - 2 × margin - count × item width) ÷ (count - 1). That gives the clear gap between items.
Worked example: five 40 mm slats
Across an 800 mm span, five 40 mm slats with a 50 mm margin at each end leave four clear gaps of 125 mm. The centre-to-centre spacing is 165 mm. Measured from the left end, the centres are at 70, 235, 400, 565 and 730 mm.
Check before drilling or cutting
Mark the two end positions first and make sure they look right on the actual workpiece. Then mark the intermediate centres from the same datum. For a jig or repeated drilling operation, test the layout on scrap and check the first and last positions before using the finished material.
Common questions
Are the end spaces the same as the spaces between items?
Not necessarily. You choose the margin at each end. The calculator then makes every internal clear gap equal while keeping those two chosen margins.
Can I use this for shelf-pin holes?
Yes, when you need a chosen number of holes across a known span. Set item width to zero. This does not replace a system-pitch template when the holes must follow a standard such as 32 mm spacing.
Can I use it as a slat or fence-picket spacing calculator?
Yes. Enter the full span, number of slats or pickets, their actual width and the margin wanted at both ends. The result gives equal clear spaces and every centre position. For railings, guards or other regulated work, check the permitted opening with the applicable building rules rather than relying on the layout alone.