What are the black diamonds on a tape measure for?
Most tape measures have a little black diamond every nineteen-and-a-bit inches, and most people who own one have never used it. It's not decoration and it's not a misprint. Justin Metzler draws it out on a whiteboard: the black diamonds on a tape measure mark 19.2 in framing layout, the third way to land 8 ft sheet goods on framing.
Applies to
- Process
- Framing — floor joists, roof trusses, wall studs
- Materials
- 4 x 8 ft (1219 x 2438 mm) sheet goods — plywood, OSB, drywall
- Setup
- Tape with framing marks (16 in highlighted, black diamonds at 19.2 in)
- Orientation
- Measured along the plate, rim or ridge from the end where the first sheet starts
- Not for
- Deciding what spacing is allowed — the joist and sheathing specs do that
Why it matters
All three common layouts divide 96 in evenly. 16 in goes in six times, 24 in goes in four times, and 19.2 in goes in five. That's the whole reason they're the common layouts: an 8 ft sheet always breaks on a framing member, so you never nail a seam to air.
19.2 in is the in-between option. Fewer members than 16 in on center, stiffer than 24 in. It shows up a lot with engineered I-joists.
Nobody can read 19.2 off a tape, though.
It isn't on the sixteenths. 19.2 in falls between 19 3/16 and 19 1/4, so the creator writes 19 3/16 in, the nearest sixteenth. The diamonds do that rounding for you at every step, so the error never piles up.
What good looks like
- Every sheet edge lands on the center of a framing member
- The fifth diamond sits on 96 in exactly
- Every mark reads off one hooked tape, not stepped off piece by piece
- The spacing matches what the joist spec and sheathing span rating allow
How to apply it
- Check what spacing you're allowed to use. The joist or truss spec and the sheathing span rating decide that, not the tape.
- Hook the tape on the end where your first sheet starts.
- Mark a member center at every diamond. To the nearest 1/16 in that's 19 3/16, 38 3/8, 57 5/8, 76 13/16 and 96 in (488, 975, 1463, 1951 and 2438 mm).
- Keep marking every 19.2 in from the same hook on longer runs. Every fifth mark lands on a sheet seam: 96, 192, 288 in.
- For 16 in on center, use the highlighted 16 in marks instead (six spaces). For 24 in, mark 24, 48, 72 and 96 in (four spaces).
Test it on your setup
- Check the tape: find the fifth diamond. It should sit on 96 in (2438 mm).
- Dry-fit a sheet on the layout before fastening. Its far edge should break on a member center.
- Count spaces, not marks: five spaces of 19.2 in, six of 16 in, four of 24 in, all across 96 in.
Exceptions & tradeoffs
19.2 in is wider than 16 in. Thinner subfloor or drywall can sag between members or run past its span rating at that spacing. Check the rating before you switch.
Not every tape has diamonds. Some brands use a different shape or colour for the same mark, and some leave it off.
Mind you, the end member sits flush with the end of the wall or floor, not centered on 0. That's fine: the first sheet starts flush on its outside face, and its far edge lands on the center of the member at 96 in.
On a metric 2400 mm sheet the same three layouts are 400, 480 and 600 mm on center (six, five and four spaces). The diamonds are an imperial-tape thing.
Common mistakes
- Using the diamonds because they're there, without checking the joist or sheathing specThe spec sets the spacing; the tape only marks it
- Stepping off 19 3/16 in five times with a short tapeThat ends 1/16 in short at 96 in — read every mark off one hooked tape
- Hooking from the wrong end so the first sheet missesStart the tape at the end where the first sheet edge lands
Frequently asked questions
- What are the black diamonds on a tape measure?They mark 19.2 in spacing, which divides an 8 ft (96 in) sheet into five equal spaces. Framers use them to lay out joists, trusses or studs so every sheet edge lands on framing.
- Why is 19.2 inches on center used?It sits between 16 and 24 in on center: fewer framing members than 16 in, stiffer than 24 in, and it still divides 96 in evenly. It's common with engineered I-joists.
- What do the highlighted numbers on a tape measure mean?On most tapes the highlighted numbers, often in red, mark 16 in on-center spacing: 16, 32, 48 and so on. Six of those spaces make one 8 ft sheet.
- Is 19.2 inch spacing allowed for floor joists?Only if the joist manufacturer's span table and the subfloor's span rating allow it for your span. The diamonds just mark the spacing; they don't make it right for every floor.
The three standard on-center spacings that divide an 8 ft sheet (16, 19 3/16 and 24 in), and that the tape diamonds mark the 19.2 in one — What are the diamonds on a tape measure for? Also, here's a brief explanation of stud and joist spacing as it relates to wall and floors, and all 8' long sheet goods. ↗ at 1:30–2:20.
Summarized and independently edited by Start Here from Justin Metzler's Facebook clip, read off the whiteboard frames and caption with no audio. The 16, 19 3/16 and 24 in layouts drawn against 8 ft sheets are his. That the diamonds mark the 19.2 in spacing is what his title and board point to; I didn't have his spoken explanation. The exact 19.2 value, the mark positions, the metric numbers, the I-joist and span-rating cautions and the stepping-off math are mine.