How long is 1 inch?
One inch equals 2.54 centimeters.
1 inch at actual size
Accurate after calibration. Approximate before calibration.
1-inch ruler from 0 to 1 inches.
Why we built this site
Every ruler page on this site ships with a one-time screen calibration — hold any bank card against the on-screen card, save, and every ruler becomes true to life on your exact display. Below each ruler you get ten real-world comparisons chosen for that length.
Screen Calibration
Place a credit card against your screen and adjust until the on-screen card matches.
Conversions
How long is 1 inch compared to an object?
United States Quarter
About 1 inchA US quarter is 0.955 inches across, close enough to an inch to work as a stand-in ruler. Authorized in 1792, it has run through dozens of reverse designs since.
Standard Small Paperclip
About 1 inchThe Gem paperclip measures about 1 inch. It is a single wire bent into two loops and has barely changed since it was patented in the 1890s.
Distal Joint of a Human Thumb
About 1 inchThe inch takes its name from the thumb, from the knuckle to the tip. Hands differ, so the average adult thumb lands near 1 inch, which is where the unit came from.
Standard Plastic Water Bottle Cap
About 1 inchA standard PET bottle cap measures about 1 inch across. The threads are sized to the bottle finish, and the cap is the one part of a 20oz bottle that is reliably that size.
Traditional Sewing Thimble
About 1 inchA metal thimble stands about 1 inch tall, worn on the fingertip. The dimples catch the needle's blunt end and stop it going through the skin.
Classic Overcoat Button
About 1 inchA four-hole overcoat button is commonly 1 inch, or about 25mm. That size is chosen to be large enough to grab through a wool buttonhole with gloves on.
Glass Shooter Marble
About 1 inchA shooter marble measures exactly 1 inch, twice the diameter of a standard 15mm playing marble. The size and weight make it the main piece in games of rings.
Standard Wire Nail
About 1 inchA standard cut nail is sold by length, and a 1-inch nail suits picture frames and light trim. Longer common sizes run 2, 2.5 and 3 inches.
Standard United States Postage Stamp
About 1 inchA US postage stamp is 1 inch tall by 1.125 inches wide, a size fixed since the 1890s. That is why the stamp is the most widely recognised object on this page.
Standard Metal Brad Fastener
About 1 inchA paper brad has a 1 inch head and a 4 inch pin. The head is pressed down to hold paper without a visible staple, and the pin is bent over at the back.
Frequently asked questions about 1 inch
What objects are about 1 inch long?
A large paperclip, a bottle cap, and the width of an adult thumb at the knuckle all land close to an inch. A US quarter falls just short at 0.955 inches across.
How many centimeters is 1 inch?
Exactly 2.54. The inch has been defined internationally as 2.54 centimeters since 1959, so 1 inch converts to 25.4 millimeters with no rounding at all.
Why does 1 inch look different on every screen?
Screens pack different numbers of pixels into the same physical space — from roughly 90 to over 500 per inch. That is why this page starts with a one-time credit-card calibration.
Is your thumb really an inch wide?
Close: most adult thumbs measure 0.9 to 1.1 inches across at the knuckle, which makes the thumb the classic quick estimate — but the calibrated ruler above is the exact answer.
Page last updated 2026-10-02
Last updated: November 2026