Half of 6 3/4 inches is 3 3/8 inches (3.375″, 85.72 mm).
How to Calculate It
Convert 6 3/4 to an improper fraction, divide by 2, then simplify. 6 3/4 = 27/4, divided by 2 = 27/8, simplified to 3 3/8.
On the Tape Measure
The mark at 3 3/8 inches (3.375″) is a standard mark on all tapes.
To find half of any tape measure measurement, enter it in TapeMath and tap the Half It button. The result appears instantly on the visual tape.