Determine how much space you will leave between each baluster within the staircase. Make a diagram of the staircase and mark each upright or baluster and indicate the position where each will go.
Use the tape measure and locate the center of the handrail. Once you have found it, mark it with the marker. This will be the central spot of the balusters.
Measure and mark the amount of space you have decided for the balusters on the handrail. If you have decided on three inches, make a mark every three inches from the central mark up and then down.
Take the measurements of the entire railing first so you are not left with an odd amount of space before the first and last balusters. If the rail is 25 inches long and you are figuring on using eight balusters, you need to mark every 3.125 inches so that the balusters are even.