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Free and accurate online ruler to measure real objects on your screen in inches, cm, and mm. Calibrate easily for actual physical size to scale.

Python
JavaScript
Java
Ruby
C#
C++
HTML5
A popular general-purpose scripting language that is especially suited to web development

Which is more popular?
Based on our record, PHP seems to be more popular. It has been mentioned 56 times since March 2021.
Website, pricing, platforms and company facts side by side.
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| Website | realsizeonlineruler.com | php.net |
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In their own words, as submitted to SaaSHub.


No description of Online Ruler yet.
We recommend LibHunt PHP for discovery and comparisons of trending PHP projects.
What each product offers, as listed by its team.


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How often each product is chosen within a category, 0–100% relative to the other.


As answered by people managing Online Ruler and PHP.
Online Ruler's answer
The calibration. Every other free online ruler I've seen skips this step entirely and just guesses your PPI, which means they're wrong on most devices. If you're measuring something where accuracy matters - a ring size, a small hardware part, a piece of fabric - being off by even 2mm causes real problems. Online Ruler is also completely free with no paywalls, no account required, and no intrusive ads covering the ruler while you're trying to measure something.
Online Ruler's answer
Most online rulers just divide your screen's CSS pixels by 96 - an assumption from the 1990s when everyone used the same CRT monitor. On a modern phone or laptop that "1 inch" can be off by 30-40%. Online Ruler actually calibrates to your specific display. You hold your physical credit card (85.60mm wide worldwide by ISO 7810 standard) against an on-screen guide and adjust until they match - at that point the tool knows your screen's real pixel density and renders a true 1:1 scale ruler. You can also calibrate by entering your screen diagonal or picking your device from a database of 150+ models.
Online Ruler's answer
People who need a quick, accurate measurement and don't have a physical ruler nearby. That's a wider group than you'd think - jewelry buyers checking ring sizes, crafters and sewers measuring fabric, 3D printing hobbyists verifying print dimensions, students doing geometry, and people shopping online who want to compare a product's listed size to something physical. The tool is available in 9 languages (English, Spanish, French, German, Portuguese, Italian, Japanese, Chinese, Russian) so the audience is genuinely global.
Online Ruler's answer
I ordered a ring online and measured my finger on an online ruler that turned out to be completely uncalibrated. Wrong size, had to return it. When I looked into why it was wrong, I found that basically every free online ruler on the internet makes the same mistake - they assume 96 DPI and call it a day. The actual pixel density of modern screens varies from about 90 PPI on a big desktop monitor to over 500 PPI on a flagship Android phone. So I built one that actually solves this with a proper calibration step. The credit card method came from realizing that one physical object almost everyone has in their pocket has globally standardized dimensions.
Online Ruler's answer
It's a free consumer tool with no accounts, so there's no customer data to pull from. But based on usage patterns and the guide content that gets the most traffic:
Jewelry buyers and makers measuring ring sizes at home Sewers and crafters measuring fabric and patterns 3D printing hobbyists verifying print accuracy Students needing a ruler for schoolwork Online shoppers comparing product dimensions to real objects
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Recommendations tracked on public social media and blogs since March 2021.


Tracking Online Ruler since Sep 2026.
The PHP website is indeed one of the worst parts of the whole ecosystem. Just look at the landingpage (https://php.net) and compare it with those of other languages. There's not a single piece of PHP code on the page. No "what is PHP",... - Source: Hacker News / 5 months ago
My initial idea was to leverage the main application’s queue worker by deploying a queue worker remotely and setting up a secure connection between them using something like Wireguard. Vigilant is written in PHP using the Laravel... - Source: dev.to / 11 months ago
I remember being 15 (18 years ago 🥲) and learning PHP. Stack Overflow wasn’t as big yet, and finding answers often meant digging through forums filled with half-baked solutions, each dependent on specific hosting configurations. There... - Source: dev.to / over 1 year ago
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