The most common mistake people make when cutting wood to specific lengths is they cut on the wrong side of the line. Following these steps will give you greater success with your cuts.
1. Use a good tape measure to measure the desired length. Make sure the tape is laying parallel with the wood and not on the diagonal.
2. Use a sharp pencil and place a single mark at the measurement.
3. Use a square and draw a line across the wood through the mark.
4. No matter what type of saw you use, be sure to cut to the outside edge of the line.
The saw kerf will take up about 1/8″. This should be taken out of the waste piece.