Board Spacing Calculator
Find equal board gaps or calculate how many full-width boards fit across your opening
Your layout
Choose a mode and enter your measurements to see the gap, board count and layout
The result describes the installed layout · Choose a gap that also suits the timber, its moisture condition and the project design
How to use the board spacing calculator
Measure the clear opening and the actual face width of your boards · Equal-gap mode divides the spare width across a set number of spaces · Board-count mode keeps your chosen gap and returns the number of full-width boards that fit
Choose how the edges should look
No edge gaps puts the first and last boards against the boundaries in equal-gap mode · Equal edge gaps adds two more spaces · Fixed clearance reserves the same measurement at each outside edge before calculating the internal gaps
In board-count mode, any remaining width is unallocated · You can divide it between the outside edges, adjust the gap or reconsider the board count before marking out
Equal-gap formulas
With no edge gaps: gap = (opening width − number of boards × board width) ÷ (number of boards − 1)
With matching gaps at both edges: gap = (opening width − number of boards × board width) ÷ (number of boards + 1)
With fixed edge clearances: subtract both edge clearances from the numerator, then divide by the number of boards − 1 · A single board needs matching edge gaps or fixed clearances that exactly fill the opening
A worked example
A 1,800 mm opening with twelve 140 mm boards leaves 120 mm for gaps · With no edge gaps, the eleven internal gaps are about 10.909 mm each · With matching edge gaps, thirteen gaps are about 9.231 mm each · With a fixed 5 mm clearance at either edge, the eleven internal gaps are exactly 10 mm
Counting boards with a chosen gap
First subtract both reserved edge clearances from the opening · Full boards = (available width + chosen gap) ÷ (board width + chosen gap), rounded down · Twelve 140 mm boards with eleven 10 mm gaps use 1,790 mm, leaving 10 mm in a 1,800 mm opening with no reserved edge gaps
Turn the result into a buildable layout
The diagram uses the calculated dimensions · Displayed measurements are rounded, so check the full run from one datum instead of accumulating a rounded gap across every board · The tool does not add spares or calculate board length, fixings or timber movement
For a practical layout method, read how to space fence boards evenly · For posts, rails and quantities across a whole fence, use the fence planner