Many carpentry and craft applications require items to be spaced evenly across a given distance. Shaker style furniture makes extensive use of evenly spaced slats, while stair rails are often supported by evenly spaced balusters or spindles. Outdoor projects, such as building a picket fence or planting a vegetable garden, also require these measurements. The trick to getting a perfectly even spacing in these applications is to measure each placement by its centre rather than its edge.
Measure the width of one baluster and the length of the rail onto which you are attaching balusters, slats or other items. Record these values.
Rail = 75 inches Baluster = 2 inches
Decide on an on-centre spacing for your items. Building codes will typically require 4 inches maximum on centre spacing. For the purposes of this example we will use a spacing of 3 inches.
Add the baluster width to both the rail length and the on-centre spacing.
75 + 3 = 78 inches for rail calculation 2 + 3 = 5 inches for baluster calculation
Calculate how many slats or balusters you need to fill the space evenly by dividing the rail calculation by the baluster calculation. Round down to the nearest whole number if necessary.
78/5 = 15.6
In this case you would round down to 15 balusters.
Subtract twice the number of balusters required from the rail calculation and divide the result by the number of required balusters, plus one.
78 - 30 = 48 48/16 = 3 inches
The on-centre spacing for the balusters or slats in this example is 3 inches.
If you have an even number of balusters, start at one end of the rail and measure toward the other end using the spacing you calculated. For an odd number of balusters, place one in the centre of the rail and measure the remaining balusters from the centre outward to the end of the rail.