Why Some Tape Measures Have Black Diamonds

Lori Dorn
September 18, 2026

Simple Things – Surprising Histories explained why some tape measures use black diamonds to mark 19.2-inch intervals, dividing an eight-foot span into five equal sections. The marks provide a visual shortcut for laying out floor joists and roof trusses.

We explain why tape measures have those black diamonds and how they are used step by step using real math and verified framing methods.

An Inside Look at How a Tape Measure Is Made

Lori Dorn

Lori is a Laughing Squid Contributing Editor based in New York City who has been writing blog posts for over a decade. She also enjoys making jewelry, playing guitar, taking photos and mixing craft cocktails.