How Long Is 1.375 Inches? 1.375 inches equals 1 3/8 inches, or 34.925 millimeters, or 3.4925 centimeters. That’s it — that’s the exact size.

But numbers on a screen don’t always mean much. This guide breaks down what 1.375 inches looks like in real life, where to find it on a ruler or tape measure, and 14 everyday objects that match this exact measurement.

Quick Answer — 1.375 Inches Converted

Here’s 1.375 inches across the units you’re most likely to need:

The math behind it is simple. Inches convert to millimeters by multiplying by 25.4, since one inch is defined as exactly 25.4 millimeters (NIST). So 1.375 × 25.4 = 34.925 mm, no rounding needed.

You’ll see this size written a few different ways depending on where you find it. Hardware packaging usually shows 1 3/8″. A digital caliper shows 1.375″. A metric spec sheet shows 34.93 mm. All three describe the same physical length.

Eighths and sixteenths of an inch are the backbone of American measuring tools, and 1.375 sits neatly on that scale — which is exactly why it shows up so often in hardware, sporting goods, and packaging.

Where Is 1.375 Inches on a Ruler and Tape Measure?

This is one of the most searched parts of this topic, and for good reason — reading a ruler accurately takes a bit of practice.

What 1.375 inches looks like on a ruler

Look at the space between the 1-inch mark and the 2-inch mark. A standard ruler splits every inch into 16 equal parts, so each small line equals 1/16 inch, or 0.0625 inches.

1.375 inches lands exactly on the sixth small line past the 1-inch mark. Count it out: 1, 2, 3 lines gets you to 1 3/16″. Keep going to the 6th line, and you’re at 1 6/16″, which simplifies to 1 3/8″ — precisely 1.375 inches.

What .375 inches looks like

The decimal .375 by itself equals 3/8 of an inch. On a ruler, that’s the distance from zero to the same sixth small mark — roughly the width of three stacked pennies, or slightly wider than a standard pencil.

Reading 1.375 on a tape measure

A tape measure works the same way as a ruler, just stretched out and often labeled with bigger fraction markings for faster reading on the job site. Contractors typically read tape measures in 1/16-inch increments, and many tapes highlight the 1/8″ and 1/4″ marks in bolder red or black to make quick reading easier.

To find 1.375 on a tape measure, locate the 1-inch mark, then count to the third small line past the 1 1/4″ mark. That’s your 1 3/8″ — the tape measure equivalent of 1.375 inches.

14 Real-Life Things That Are 1.375 Inches Long

Numbers stick better when you can picture them. Below are everyday objects that match this measurement almost exactly, grouped by category.

Hardware and Fasteners

A standard hex nut used in construction hardware often measures 1.375 inches across its flat sides, particularly in the 3/4-inch bolt size range under ANSI fastener standards.

Wood screw heads on heavy-duty deck screws also land close to this width, which matters when picking countersink bits.

Plumbing has its own connection to this size too. Under the Nominal Pipe Size (NPS) system used across North America, a pipe labeled “1-inch nominal” actually has an outside diameter of 1.315 inches — remarkably close to 1.375 inches, which is why plumbers often double-check actual OD with calipers rather than trusting the nominal label alone (Wikipedia: Nominal Pipe Size).

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Office Supplies

A jumbo paper clip measures close to 1.375 inches along its longest edge.

A medium binder clip, the kind found in nearly every office supply drawer, measures about the same across its metal frame.

Games and Sporting Goods

Regulation table tennis balls are 40 mm in diameter under International Table Tennis Federation rules — that converts to 1.575 inches, but the older pre-1999 standard ball size (38 mm) sits closer to 1.5 inches, showing how this category has shifted with rule changes.

Casino dice used in regulated Nevada gaming halls commonly measure 1.375 inches per side, sized larger than standard dice specifically so pit bosses and overhead cameras can track rolls clearly.

A castle-style golf tee, favored for fairway wood shots, stands about 1.375 inches tall from base to cup.

Food and Natural Objects

A large English walnut in its shell often measures close to 1.375 inches at its widest point — premium “jumbo” grade walnuts are sorted by size for exactly this reason.

Colossal Cerignola olives, an Italian variety sold at specialty grocers, run about the same length from stem to tip.

Everyday Tech and Household Items

A AA battery measures 14.5 mm in diameter under IEC standard 60086 — just a hair over 1.375 inches, close enough that the two numbers are often used interchangeably in casual comparisons.

Prescription pill bottle caps are frequently sized around 1.375 inches in diameter, a dimension shaped partly by child-resistant packaging requirements set by the Consumer Product Safety Commission.

Fashion and Sewing

Large coat buttons, the kind used on wool overcoats and peacoats, commonly measure 1.375 inches across — a size tailors have used consistently since mid-20th-century outerwear became standardized.

Practical Ways to Measure or Estimate 1.375 Inches

Sometimes you need this measurement and there’s no ruler in sight. A few reliable shortcuts:

Use your thumb. The width of an average adult thumb at the knuckle is close to 1 inch, so 1.375 inches is just slightly more — about a thumb-width plus a third.

Use a known object. A medium binder clip or a AA battery, both listed above, gets you within a hair of the exact size without any tool.

Use a stack of coins. Three US pennies stacked flat measure roughly 1/2 inch combined, giving a rough visual anchor for scaling up to 1.375 inches.

None of these replace an actual ruler or digital caliper for precision work, but they’re useful for a fast field estimate.

Why 1.375 Inches Matters in Real-World Use

This isn’t a random number. Fractional inch sizing — halves, quarters, eighths, sixteenths — has driven US manufacturing tolerances since the adoption of the inch-pound system, and 1.375 (or 1 3/8″) sits neatly within that sixteenth-based grid.

That’s precisely why it shows up repeatedly across unrelated industries: hardware, sporting goods, packaging, and fashion. Manufacturers didn’t coordinate on this size — they all default to the same measuring grid, because customary US units are built around eighths and sixteenths rather than decimals.

Engineers working with ASME-standard fasteners and plumbing components rely on this same sixteenth-inch grid for tolerances, which is part of why hardware sizes tend to repeat across brands rather than vary randomly.

FAQs

What does 1.375 inches look like on a ruler?

It sits between the 1-inch and 2-inch marks, exactly on the sixth small line — the same point labeled 1 3/8″ on a fractional ruler.

What does .375 inches look like?

It equals 3/8 of an inch, or about the width of three pennies stacked together — roughly the thickness of a standard pencil.

How long is 1.375 in inches?

1.375 is already expressed in inches. As a fraction, that’s 1 3/8 inches; in millimeters, it’s 34.925 mm.

What is 1.375 on a tape measure?

It’s the third small mark past the 1 1/4″ line, labeled 1 3/8″ on most fractional tape measures used in the US.

Conclusion

1.375 inches — or 1 3/8 inches — is a small but common measurement hiding in plain sight, from your desk drawer to your toolbox. Once you know where it sits on a ruler and which everyday objects match it, estimating this size becomes second nature, no measuring tape required.

Timmy Zeeshan

Timmy Zeeshan is the founder and lead editor of CM Measurement, where he writes and maintains a growing library of unit conversion tools and practical measurement guides. With a background in engineering and a long-standing interest in everyday math problems, Timmy started CM Measurement after growing frustrated with cluttered, ad-heavy converter websites that made simple conversions harder than they needed to be.