Half of 1 1/2 inches is 3/4 inches (0.75″, 19.05 mm).
How to Calculate It
Convert 1 1/2 to an improper fraction, divide by 2, then simplify. 1 1/2 = 3/2, divided by 2 = 3/4, simplified to 3/4.
On the Tape Measure
The mark at 3/4 inches (0.75″) is a standard mark on all tapes.
Why 1 1/2″ Is Everywhere in Woodworking
1 1/2″ is the actual thickness of all nominal 2× dimensional lumber — every 2×4, 2×6, 2×8, and 2×10 is exactly 1 1/2″ thick. This makes halving it a constant calculation when cutting lap joints, locating dado centers, and planning any joinery that references a board face.
When You Need Half of 1 1/2″
Half of 1 1/2″ is 3/4″ — the thickness of standard 3/4″ plywood. A halved 2× perfectly matches plywood thickness, which is the basis for box joints and dado-and-rabbet joinery in cabinet construction. Door hinges are also 1 1/2″ tall; 3/4″ is the standard hinge setback from the door edge.
Finding 3/4″ on the Tape
3/4″ is one of the most prominent marks on any tape — 12 marks from zero counting 16ths, or 6 marks counting 8ths. It sits exactly halfway between 1/2″ and 1″, making it one of the fastest marks to find on a busy job site.