CSS Unit Converter — px ↔ rem ↔ pt ↔ cm
Convert between CSS units: px, rem, em, pt, cm, mm, in, vw, and vh.
How it works
- 1Type or paste in the value (e.g. 16px) field
- 2Conversion happens instantly in your browser
- 3Copy the result with one click
What to do next
About CSS Unit Converter
CSS Unit Converter is the kind of utility you bookmark and reach for when you need it. Convert between CSS units: px, rem, em, pt, cm, mm, in, vw, and vh. It loads quickly, works on any modern browser, and produces a result you can download or copy in a single click.
The processing pipeline is straightforward: your input is parsed by standard browser APIs, transformed according to the options you select, and serialised back into a downloadable result. The 0 MB per-file ceiling matches what a typical browser tab can handle without paging to disk.
The right moment to reach for CSS Unit Converter is when you have a focused developer utility job that fits inside a browser tab. Open the page, drop in the file or paste your input, choose the options that matter, and the tool returns the result.
Because everything runs in the page, the tool scales the same way for one user or a million — there is no per-user backend cost. The page is static, the engine is the same JavaScript bundle for every visitor, and the work happens on the visitor's own device. That keeps the tool free and keeps it fast on the first interaction.
The only practical limit is the 0 MB per-file ceiling, which keeps the tool responsive across a wide range of devices. Run the tool ten times in a row, run it ten thousand times — it behaves the same way and produces the same quality of result.
Even on its own, CSS Unit Converter composes well with the rest of your toolkit. The output is a standard developer file that opens in any program that handles the format, so the result of one run can become the input to whatever step you use next.
CSS Unit Converter fits naturally into the workflow of QA engineers writing repro cases and students learning new languages, both of whom typically need a fast result inside the browser. There is no learning curve to budget for: anyone who has used a typical web upload form can complete a run on the first try.
Once the engine finishes, the output is offered as an immediate download. There is no preview gate, no email-wall, and no "register to download" intermediary — the file is yours the moment it is ready.
CSS Unit Converter keeps the control set focused. Every option on the page is there because a real workflow needs it, and the defaults aim at the most common case so a first-time user can get the right output without changing any settings.
CSS Unit Converter is structured around the idea that a useful tool should be its own page. Open the page, do the work, close the tab — the page is the entire product. There is no onboarding flow because there is nothing to onboard into.
Useful patterns when working with CSS Unit Converter: keep the input file open in another tab so you can compare against the result; give the output file a descriptive name when saving so you can find it later (the default name is sensible but generic); and treat each run as independent — the tool has no concept of "history", which means you cannot accidentally pollute one job with leftovers from another.
CSS Unit Converter is built around the moment of need: a focused page you open when you have a specific task, complete the task, and close. The catalog contains many adjacent tools so the same model serves the surrounding parts of a typical developer utility workflow.
If CSS Unit Converter appears to hang, the engine is almost certainly still working — large inputs simply take longer to process inside a browser than they would on a server with multi-core scheduling. For inputs near the 0 MB cap, give it up to a minute on a typical laptop before assuming something is stuck.
That is the whole tool. Use CSS Unit Converter for as long as it stays useful to you, and if it does, the catalog has many more tools built the same way. Each applies the same single-purpose discipline, so the way you used this page transfers to the next one you try.
How it works
- 1Open CSS Unit Converter in your browser. The page loads quickly and the tool is ready to use the moment it becomes interactive.
- 2Select the developer file you want to process — drag-and-drop and the file picker both work.
- 3Adjust the options to match what you need. Sensible defaults cover the most common case, so you can usually skip this step.
- 4Trigger processing. standard browser APIs reads your input, applies the transformation, and writes the result back into the page.
- 5Download the result. The file is generated in your browser and saved through your normal download flow.
- 6Run additional jobs as needed. The same controls and defaults apply on every run.
Common use cases
- Generate boilerplate from a single specification line using CSS Unit Converter.
- Validate a config blob before pushing to staging.
- Encode binary content for transport in a JSON body.
- Decode a token to confirm its claims during a debugging session.
- Inspect a payload during local development without writing a script.
- Generate a quick fixture without leaving the browser.
- Compare two API responses to spot a regression.
- Inspect a regex against a test string before committing it.
- Convert between data formats while wiring up an integration.
FAQ
What base font size is used?
16px — the browser default. rem and em conversions assume 1rem = 16px.
What about vw and vh?
Viewport units are estimated based on a 1920×1080 reference viewport for approximate conversions.
Are em and rem the same?
rem is relative to the root font size; em is relative to the parent. This tool treats both as 16px-based.
Can I change the base size?
The tool uses the standard 16px base. For custom bases, multiply the rem output by your base/16.
How accurate is pt conversion?
Based on the CSS standard: 1pt = 1/72 inch, 1in = 96px, so 1pt ≈ 1.333px.
Is my data safe?
All processing happens in your browser.
Can I process multiple files at once with CSS Unit Converter?
CSS Unit Converter processes one input at a time by design — it keeps memory usage predictable on lower-end devices and makes results easier to verify. To handle a folder, run the tool once per file; the page stays loaded between runs and remembers your last-used settings, so the second run is essentially instant.
Why did CSS Unit Converter reject my input?
Failures usually fall into one of three buckets: the input is in an unsupported format, the input is over the size cap, or the input is structurally malformed (a truncated download, a partial export, or a stream the engine does not recognise). The first two are easy to confirm — check that your file is in a supported format and that it is below 0 MB. For the third, opening the file in its native viewer first is the fastest way to confirm the source is intact.
Does CSS Unit Converter require a browser extension or plug-in?
No installation is needed. CSS Unit Converter runs as a normal web page, with no browser extension, no native helper, and no separate desktop client to download. That is partly a privacy choice — extensions can request broad permissions, while a regular page is sandboxed by default — and partly a convenience one: you can use CSS Unit Converter on any computer you have temporary access to without leaving anything installed on it.
Do I need a specific browser to use CSS Unit Converter?
CSS Unit Converter works in any modern browser released in the last few years — Chrome, Edge, Firefox, Safari, Brave, Arc and the major Chromium derivatives are all supported. The underlying engine relies on widely-supported web APIs, so there is nothing exotic to install. If you are on a very old browser version and the tool fails to load, updating to the latest release of your preferred browser is the only fix needed.
Can I use CSS Unit Converter on iOS or Android?
CSS Unit Converter runs in any modern mobile browser — Safari, Chrome, Firefox and the in-app browsers in most messaging apps all support the underlying APIs. Performance depends on the device: a recent phone handles typical inputs nearly as fast as a laptop, while older devices may take a few seconds longer near the 0 MB ceiling. The interface lays out cleanly on small screens, so you do not need to pinch-zoom to see the controls.
How is CSS Unit Converter different from desktop apps that do the same thing?
Desktop apps usually have more advanced features but require installation, maintenance and (often) a licence. Paid online tools are convenient but route your file through their servers and gate downloads behind accounts. CSS Unit Converter sits in between: free, instant, and private, but intentionally narrow in scope. For one-off jobs and the common developer utility operations, it is usually the lowest-friction choice; for highly specialised work, a dedicated app is still the right answer.
Is the source for CSS Unit Converter available?
CSS Unit Converter is a static page running an open-source engine in your browser, so a typical corporate firewall does not get in the way as long as it allows JavaScript to load from Favtoo. For teams that need to host it themselves on an internal network, the underlying engine (standard browser APIs) is open-source and can be packaged into a private build with the same behaviour. Reach out via the Contact page if that is something you are exploring.
Will CSS Unit Converter keep working if my Wi-Fi drops mid-task?
Once the page is loaded, CSS Unit Converter can complete jobs without an active internet connection — the engine is bundled with the page, so there is no per-job network call. The initial page load does require a connection (to fetch the static assets), but after that you can disconnect entirely and the tool will still work. This is a side-effect of the local-first architecture, not a deliberate "offline mode" feature.
What permissions does CSS Unit Converter need to function?
CSS Unit Converter only needs the standard web platform — file picker access for the inputs you choose to load, and optionally clipboard access if you copy the result rather than downloading it. There is no microphone, camera, geolocation or background-permission request, because none of those are needed for the work the tool does.