Legal

Privacy Policy

Last updated: September 23, 2026

The short version

This site keeps one thing on your device: a calibration record, so the ruler is still true the next time you open it. The record holds measurements of your display and nothing about you. There are no accounts, no cookies, no analytics of any kind and no uploads. We collect nothing, so there is nothing we could sell. Everything the tools compute happens inside your tab.

The one thing that is stored, in full

When you calibrate, one entry is written to your browser's local storage for this site, under the name realsizer.calibration. It is a single versioned record and this is all of it:

• the density you measured, as device pixels per millimeter;
• which reference object you matched, which edge of it, and which way up you held it;
• the error band that object and edge earn;
• the second reference and the agreement percentage, if you ran a cross-check;
• the date and time of the match;
• a snapshot of what your browser was reporting at that moment, which is ten values: the pixel ratio; the native pixel width and the native pixel height of the screen; the width of the browser's own chrome and its height; the viewport width in device pixels; the layout scale and the pinch scale; the measured width of a CSS inch; and one value that is not a display property at all. If a mouse has moved across the page, the record keeps the ratio between how far the pointer travelled on the screen and how far it travelled inside the page, which is how the page catches a zoom the browser declines to report. That last one is a ratio of two distances and nothing else: no pointer position, no path, and no timing is kept.

Those ten values are the witnesses, and the list above names every one of them. They let the page tell a change it can correct for, such as a page zoom or a display-scaling change that the browser reports through its pixel ratio, from a change it cannot. After a change it cannot correct for, the ruler drops out of its calibrated state and asks you to match the card again. The methodology page explains what each one catches.

The record is not personal data. It describes a display and holds no identifier, name, address or account. Your browser writes it and reads it, and it is never transmitted: the Content-Security-Policy described below blocks requests to any outside origin. Display characteristics and the pointer ratio above are signals used for fingerprinting elsewhere on the web. This site reads them only from your own device, and only to keep your own ruler true.

Removing it

The ruler page has a Discard calibration control that deletes the record immediately. Clearing site data for this domain in your browser settings does the same. Each browser on each device keeps its own storage, so the record is not shared between your phone and your laptop (which have different displays anyway) or between two browsers on one machine.

Browser storage is separated by origin, so a calibration made on any other website, including any other site we operate, cannot be read here, and one made here cannot be read there.

If your browser will not allow storage at all (in a private window, or with a setting that blocks it), the tools still work. A match calibrates the ruler for that visit only, and a neutral note on the page says it was not saved.

What is not stored

No cookies are set by this site, for any purpose. There is no session storage, no IndexedDB, no service worker and no offline cache. There is no sign-up, no login, no email capture and no list. There is no file picker, no camera access, no microphone access and no clipboard read anywhere on the site. The tools compute from a number you produce by dragging an outline, and they take in nothing else.

No analytics

This site runs no analytics, and neither does any other site we operate. There is no beacon, no tag manager, no pixel and no visitor counter. Your browser enforces this: the Content-Security-Policy served with every page allows connections to this origin alone, so a request to any outside origin is blocked.

Hosting and server logs

The site is served by Cloudflare Pages. Like any web host, Cloudflare processes standard technical data (IP address, user agent, requested URL) to deliver pages and protect against abuse, subject to Cloudflare's privacy policy. A page request is the only thing any server sees, and your calibration is not in it.

Advertising

The site shows no advertising and loads no advertising script. Some pages reserve empty ad slots between sections of text, and none of them sits inside or beside a ruler face or a calibration control.

Email

If you email hello@realsizer.com, your address is used solely to reply and is not added to any list. Please do not send photographs of the card you calibrate with. No step here needs one, and the Contact page lists what is useful in a report.

Children

The site is a general-audience utility and does not knowingly collect personal information from anyone, including children.

Changes and contact

The date at the top shows when this policy last changed. Privacy questions: hello@realsizer.com.