Legal
Privacy Policy
Last updated: August 9, 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. It holds measurements of your display and nothing about you. There are no accounts, no cookies, no analytics of any kind, no uploads, and nothing that could be sold — we could not; we do not collect it. 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 millimetre;
- 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 ratio between how far the pointer travelled on the screen and how far it travelled inside the page, which is how a zoom the browser declines to report is caught. That last one is a ratio of two distances and nothing else: no pointer position, no path, and no timing is kept.
Those last items are the witnesses, and the list above is the whole of them — ten fields, named individually rather than described in general, because a summary of a stored record is not the same thing as the record. They exist so that the page can tell the difference between a change it can correct for — a page zoom or a display-scaling change that the browser reports through its pixel ratio — and a change it cannot, in which case it drops out of its calibrated state and asks you to match again rather than continuing to look confident. The methodology page explains what each one catches.
Two things this record is not. It is not personal data: it describes a display, not a person, and there is no identifier, name, address or account in it. And it is not sent anywhere — it is written by your browser, read by your browser, and never transmitted, which is a property enforced below rather than a promise made here. Signals of this kind — display characteristics, and the pointer ratio named above — are used for fingerprinting elsewhere on the web, so it is worth being precise: they are collected here only from your own device, only to keep your own ruler true, and they never travel.
Removing it
The instrument pages carry a Discard calibration control that deletes the record immediately. Clearing site data for this domain in your browser settings does the same. The record is per browser and per device — it is not shared between your phone and your laptop, or between two browsers on one machine, because each keeps its own storage and each is looking at a different display anyway.
A calibration made on any other website is not readable here, and one made here is not readable there. That includes any other site we operate: browser storage is separated by origin, so a ruler calibrated on another domain cannot carry across to this one, and nothing on this site implies that it does.
If your browser will not allow storage at all — a private window, or a setting that blocks it — the tools still work. The calibration lasts for that visit only, and the page says so in a neutral note. Being unable to save is not a failure of the measurement and is not treated as one.
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 there is nothing else for them to ingest.
No analytics, at all
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. That is enforced by the browser rather than by intention: the Content-Security-Policy served with every page pins connections to this origin alone, so a request to any outside origin fails closed. If analytics ever appears to be broken on this site, it is broken on purpose. We accept not knowing how many people visit.
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 — in order 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 currently shows no advertising. If that changes, this policy will be updated first, any advertising will comply with applicable consent requirements, and a consent choice will be presented where the law requires one. Two things will not change: nothing about how the tools work, and where advertising may sit. No advertising will be placed inside or beside a ruler face or a calibration control.
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; there is no step here that needs one, and Contact sets out what is actually 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
If this policy changes, the date at the top changes with it. Privacy questions: hello@realsizer.com.