In this video, This Old House general contractor Tom Silva shows how to quickly divide any length in half—without using math.
1. Measure the width of the board, then choose a slightly larger dimension that's easily divisible by two. For example, if the board measures 37⅝ inches, round it up to 40 inches.
2. Pull a tape measure diagonally across the board until the 40-inch graduation aligns with the edge of the board.
3. Make a pencil mark at the 20-inch graduation line, which is half of 40. That marks the exact center of the 37⅝-inch board.
4. You can also find the center using two tape measures.
5. Pull one tape measure across the board from one edge, then pull the second tape from the opposite edge.
6. Find where the point along the tapes where two identical measurements align with each other. That's the exact center of the board.