Set up two sawhorses, between 4 and 6 ft. apart. Ensure they sit on firm, level ground. Place a counter top — finished side up — on top of the sawhorses.
Pull a tape measure across the exposed side of the counter top. Make a pencil mark on the top at the required length.
Hold the base of a combination square against the edge being trimmed. Extend the square’s blade until its end aligns with the pencil mark. Set the end of a pencil against the end of the square blade. Pull the pencil and combination square along the edge to draw a dark pencil line. Drag the pencil and square along the backsplash to complete the cut line.
Hold the counter top steady with your non-dominant hand. Align the blade of a fine-cut handsaw with the end of the pencil farthest from you. Work the saw in a back-and-forth motion while steadily pulling the saw toward you. Stop cutting when you reach the corner where the counter top and backsplash connect.
Stand the counter top on the backsplash. Support the piece being cut from the counter top with your non-dominant hand while you cut through the backsplash. Slide a wood file across the cut to remove all rough edges.