Let’s clear the confusion right at the start.
.625 inches equals 5/8 of an inch.
That’s the direct answer. If you’ve ever come across .625 in inches on a ruler, blueprint, tool spec, or product description and paused for a second, you’re not alone. This number looks awkward as a decimal, but it represents one of the most common fractional measurements used in real life.
Once you understand where .625 comes from and how it fits into everyday measuring, it stops looking strange and starts feeling familiar.
What Does .625 Inches Actually Mean?
At first glance, .625 inches looks like a random decimal. It’s not. It’s simply a fraction written in another form.
The Fraction Behind .625
0.625 inches is the decimal form of 5/8 inch.
Here’s how the math works:
- 1/8 inch = .125
- 2/8 inch = .25
- 4/8 inch (1/2) = .5
- 5/8 inch = .625
So whenever you see .625, think five-eighths of an inch.
That one mental switch makes everything easier.
Why 5/8 Inch Is Such a Popular Measurement
Five-eighths of an inch hits a practical middle ground. It’s thicker than half an inch but not as bulky as three-quarters.
Common Uses of .625 Inches
- Bolts and fasteners
- Drill bits
- Tool shafts
- Furniture hardware
- Plumbing components
- Mechanical parts
Because it’s widely used in manufacturing and engineering, this measurement often appears in decimal form instead of as a fraction.
How .625 Inches Looks on a Ruler
If you’re holding a ruler, this becomes very simple.
On a standard inch ruler:
- Each small mark represents 1/8 inch
- Count five marks from zero
- The fifth mark is 5/8 inch (.625 inches)
It sits just past the half-inch mark and before the three-quarter-inch mark.
Once you spot it a few times, your eye learns exactly where it belongs.
Decimal Inches vs Fractional Inches
So why not just stick to fractions?
Why Decimals Are Commonly Used
- Easier for calculations
- Preferred in engineering and machining
- Cleaner in CAD software and spreadsheets
- Avoids fraction simplification
Why Fractions Still Stick Around
- Easier to read on physical rulers
- Common in construction and DIY
- More intuitive for quick measuring
That’s why .625 inches and 5/8 inch are both correct—and often used interchangeably.
Is .625 Inches Bigger Than 1/2 Inch?
Yes, and by a noticeable amount.
Let’s compare:
- 1/2 inch = .5
- 5/8 inch = .625
- 3/4 inch = .75
Five-eighths of an inch sits comfortably between half an inch and three-quarters of an inch, making it ideal when 1/2 feels too thin and 3/4 feels too thick.
Converting .625 Inches to Other Units
Sometimes inches aren’t enough, especially when working with metric specifications.
.625 Inches to Millimeters
Using the standard conversion:
- 1 inch = 25.4 mm
- .625 × 25.4 = 15.875 mm
So:
.625 inches = 15.875 millimeters
This exact value is important in precision work, where rounding too early can cause parts not to fit correctly.
Why Precision Matters With .625 Inches
In casual situations, people sometimes round .625 to 0.63 or call it “about 5/8.” That’s fine—until precision matters.
When Precision Is Critical
- CNC machining
- Engineering drawings
- Automotive components
- Tool manufacturing
- Tight mechanical assemblies
In these cases, .625 inches is not the same as .63 inches.
When Approximation Is Usually Acceptable
- Woodworking
- Home improvement projects
- Rough construction
- Visual alignment
The trick is knowing which situation you’re in.
Why .625 Inches Confuses So Many People
The confusion usually comes from switching formats.
You might see:
- 5/8 inch on a ruler
- .625 inches in a spec sheet
- 15.875 mm in a technical document
They’re all the same measurement—just written in different systems.
Once you recognize that, the confusion disappears.
Quick Comparison With Other Common Sizes
Here’s how .625 inches fits among familiar measurements:
- .5 inches = 1/2 inch
- .625 inches = 5/8 inch
- .75 inches = 3/4 inch
- 1 inch = 1 inch
Seeing it in order helps lock it into memory.
A Simple Trick to Remember .625
Here’s an easy way to remember it:
- Think in eighths
- Half an inch is 4/8
- Add one more eighth
- 5/8 = .625
Once that clicks, you won’t forget it.
Real-Life Situations Where You’ll See .625 Inches
You’re likely to run into this measurement when:
- Buying drill bits or fasteners
- Reading assembly manuals
- Measuring shaft or pipe sizes
- Working with mechanical tools
- Comparing metric and imperial specs
Knowing exactly what it means saves time, money, and frustration.
Final Answer (Clear and Simple)
Let’s wrap this up cleanly.
.625 inches equals 5/8 of an inch.
It’s a common, practical measurement that shows up in tools, hardware, and designs more often than people realize.
Now that you know exactly what .625 in inches means, you can read measurements with confidence—and without stopping to second-guess yourself.
