Online Tool Store
· 5 min read
3 Font Size Converter Tools, Compared Honestly
Heshan Fernando
Co-founder & COO
A design handoff gives you font sizes in points or pixels, but your CSS uses rem — and you want the correct converted value, not a rough mental-math guess that throws off your type scale.
These tools all do the core conversion correctly; the real differences show up in how many units they cover, whether they handle a whole block of CSS at once, and whether you get a live preview of how the converted size actually looks.
How to judge a font size converter tool
Covers all the units you actually use. px, pt, em, rem, and percent — a tool limited to just px-to-rem doesn’t help when a spec hands you points.
Lets you set a custom root font size. The default 16px root doesn’t apply everywhere; being able to change it and have every conversion update is important for real projects.
Batch or bulk conversion. Pasting a whole block of CSS and getting every value converted at once beats converting numbers one at a time.
Runs locally. A font-size number is trivial content, but there’s no reason it needs a server round trip either.
The comparison
| Tool | Best for | Free tier | Watch out |
|---|---|---|---|
| Testsigma | Batch CSS conversion plus responsive live preview | Free, no signup | Focused on px/rem — not the full px/pt/em/rem/percent set |
| pxtorem.us | True bidirectional live conversion as you type | Free, no signup | Primarily px/rem-focused, with pt and percent as separate related tools |
| Made Good Designs | px, rem, em, and pt in one converter, fully local | Free, no signup | No percent unit support |
| Font Size Converter | px, pt, em, rem, and percent with live text preview | Free, no signup | No batch/bulk CSS-block conversion |
Facts checked August 2026; tools change their plans.
Testsigma
Testsigma converts px and rem bidirectionally, but its standout feature is pasting an entire CSS code block and getting a converted version back at once, alongside a live responsive preview panel showing how text and layout scale across different viewports, plus a custom root font size that updates every conversion.
It isn’t for someone needing every CSS size unit in one place — it’s built specifically around the px/rem pairing rather than pt, em, and percent together.
pxtorem.us
pxtorem.us converts px to rem with no button to press — entering a value in either field updates the other instantly and automatically — with a customizable base font size, conversion reference tables, and related tools for px-to-em, percentages, viewport units, and points.
It isn’t for someone who wants all five units combined in a single converter — px/pt/em/percent conversions live as separate tools on the site rather than one unified interface.
Made Good Designs
Made Good Designs converts between px, rem, em, and pt in one tool, with a configurable root font-size, live calculation as you type, a quick-reference table for common values, and processing that’s entirely browser-based with nothing uploaded or logged.
It isn’t for someone who needs percent as a unit option — the tool covers four units but doesn’t include percent-based font sizing.
Font Size Converter
Our tool converts font sizes between pixels, points, em, rem, and percent, with a live text preview and an adjustable base font size — entirely in your browser.
A real limitation: it converts one value at a time rather than an entire pasted CSS block — for batch-converting many values across a stylesheet at once, Testsigma’s paste-a-CSS-block feature is the better fit.
Which one to pick
If you need all five common CSS size units in one place with a live text preview, use our Font Size Converter.
If you’re converting an entire CSS file’s worth of values at once, use Testsigma.
If you just want the fastest possible single-value px-to-rem lookup, use pxtorem.us.
If you want px, rem, em, and pt together with a strong privacy note, use Made Good Designs.
How to do it with Font Size Converter
- Open the Font Size Converter.
- Enter a font size and choose its unit (px, pt, em, rem, or percent).
- Set your base font size if it isn’t the default, and read the converted value with a live text preview.
Browse the full tools directory for more free, browser-based converters.
Frequently asked questions
Is there a free font size converter that doesn’t need an account?
Yes. Our Font Size Converter and all three alternatives here convert font sizes without requiring signup.
Why does rem depend on a “base font size” but px doesn’t?
Pixels are an absolute unit — 16px is always 16px regardless of context. Rem is relative to the root element’s font size, so 1rem equals whatever that root size is (commonly 16px by default, but configurable) — which is exactly why these converters let you set a custom base font size rather than assuming one fixed value.
Should I use rem or em for font sizes in CSS?
Rem is generally recommended for font sizes because it scales consistently from a single root value and respects a user’s browser font-size setting for accessibility, while em is relative to the parent element’s font size and can compound unexpectedly in nested components. Em still has valid uses for spacing that should scale with a specific element’s own font size, as covered in MDN’s CSS values and units reference.
Final thought
For consistent, accessible typography, converting a design spec’s px or pt values into rem correctly matters more than doing it fast — pick a tool that covers the exact units your project uses rather than settling for a partial converter.