About InchRuler.com
Last reviewed on 2026-04-23.
InchRuler.com is an independent, free-to-use web utility that puts a calibrated ruler on your screen. The goal is narrow and practical: measure small, everyday objects in inches or centimeters without having to dig a tape measure out of a drawer. The site has no account system, no paywall, no subscription tier, and no file uploads. You open it, calibrate once, and use it.
Who the site is for
Most visitors arrive with a simple, time-sensitive question: how wide is this screw, how long is this photo, how thick is that bead, how big is a 6 mm or a quarter of an inch in real life? The audience is broad — hobbyists, crafters, students, parents helping with homework, people checking jewelry sizes, office workers sizing print layouts — and the common thread is wanting a quick answer without installing anything.
What the site covers
The home page is the ruler itself. Around that tool, the site publishes short, plain-language reference material on the handful of topics that actually matter for getting useful measurements on a screen:
- Calibrating an on-screen ruler — step by step, with two methods and troubleshooting.
- Screen PPI, DPI, and device pixel ratio — what these numbers mean and why they matter.
- Inches ↔ centimeters — a conversion reference for common values.
- Millimeters ↔ inches — the same for millimeters.
- How accurate is an on-screen ruler? — realistic expectations, and when to reach for a physical tool instead.
Content that isn't about measurement, screens, or rulers is intentionally out of scope. Adjacent-but-off-topic material — unit conversions for temperature, weights, currencies, cooking volumes — belongs on sites that specialize in those topics.
Editorial approach
Every page on the site is written to answer a specific question someone might actually be typing into a search bar. We try to:
- Be exact where exactness matters. Conversions use the official definition (one inch = 25.4 mm, by international agreement since 1959). Reference dimensions — like the 85.60 × 53.98 mm ID-1 card used for credit-card calibration — are taken from published standards.
- Be honest about limitations. An on-screen ruler is an estimation tool. We say so in plain terms on the accuracy and disclaimer pages.
- Skip fluff. No padding, no "in today's fast-paced world," no invented statistics. Pages should be short enough to read in a coffee break and long enough to actually answer the question.
- Correct mistakes. If a factual error is pointed out through the contact page, we fix it and update the "Last reviewed" date.
How the content is produced
Pages are written by the site operator, drawing on published reference material (ISO/IEC standards for card dimensions, manufacturer specifications for device resolutions, web standards for how CSS pixels are defined). AI tools are used sparingly for proofreading and structure; every published sentence is reviewed for factual accuracy before it goes live. When a page is updated, the "Last reviewed" date at the top of the page is updated with it.
How the tool works, in one paragraph
The ruler is drawn as SVG at runtime, one tick at a time, based on a single stored value: how many CSS pixels correspond to one inch on your screen. You can set that value by picking a known device from the quick-calibration dropdown (which applies a hard-coded PPI for that model), by entering your screen's diagonal size (which lets the app compute PPI from the reported resolution), or by matching a credit card against a reference rectangle (the most reliable method, because the card's physical size is standardized). The value is saved in your browser's local storage and used the next time you visit.
How the site is funded
The site carries advertising through Google AdSense. That is the only source of revenue, and it's what keeps the ruler free, ad-supported rather than subscription-gated. Details about the data used to serve those ads, along with opt-out links, are in the privacy policy and the cookie policy.
Independence
We are not affiliated with any ruler manufacturer, measurement-instrument brand, screen manufacturer, or device vendor. Device presets in the quick-calibration dropdown exist only because their screen specifications are publicly published; inclusion is not an endorsement.
Contact and feedback
Corrections, bug reports, and feature requests are welcome at the contact page. Questions about privacy go to [email protected]. General mail goes to [email protected].