Converters

Tools that change a file from one format to another. The distinction that matters is where the work happens: an uploading converter sends your file to a machine you do not control and meters what it gives back, while a client-side one runs in your browser and cannot meter anything.

Format conversion that runs on your machine. No upload means no queue, no daily limit, no account, and no copy of your file on someone else’s disk.

The trade is that some conversions genuinely cannot be done this way. Those are named on each page rather than faked.

"Nothing is uploaded" has stopped being a differentiator for image tools — most of the good ones run locally now. What none of them removed is the file count. Squoosh, the reference implementation of the idea, still handles one image at a time. Caesium caps a session at ten. TinyPNG’s web tool stops at twenty, because behind it is a server somebody pays for.

There is no server in this path, so the cap has no reason to exist. The honest framing is not "no limits" but your device’s limits rather than ours — which is also why images are processed one after another instead of all at once. Decoding several large photographs simultaneously is the fastest way to exhaust a phone’s memory and lose the tab.

• Batches with no ceiling

  There is no server time to ration, so nothing is rationed. Files run one after another rather than in parallel, because that is what stops a phone running out of memory halfway through a folder.

  Squoosh has no batch mode at all; Caesium caps a session at ten files and TinyPNG’s web tool at twenty.

• Optimising is not the same as re-encoding

  Most browser tools decode your file onto a canvas and ask the canvas to write it back out. That is the right trade for changing a format and the wrong one for making a file smaller: a general-purpose encoder in a hurry makes very different choices from one whose entire job is to find the smallest legal encoding of the same pixels.

  Measured here: a 21,493-byte flat interface graphic came back out of a canvas PNG encode at 38,905 bytes, 81% larger. The same source through oxipng produced 3,350 bytes with every pixel identical.

• A quality number is one encoder’s private dial

  Two encoders set to the same quality value have not discarded the same amount of information, so comparing them at the same number compares nothing. What you get instead is the two images at the same size with the real byte figure under each.

  On identical pixels, MozJPEG at quality 75 produced 113,935 bytes against Chromium’s 139,476 — 18% smaller — and at quality 92 produced 188,448 against 176,567, 7% larger.

• The canvas ceiling is handled rather than hit

  Past the browser’s canvas limit there is no error and no warning: you get a file of the right dimensions containing nothing. Every allocation is clamped first, including the intermediate canvases, and the readout states the size you actually got.

  Canvas dimensions are capped near 8192 pixels a side and about 16 megapixels in total on iOS before 2024.

1. 1

   Decide whether you want a different format or a smaller file

   They are different jobs with different tools. Converting a WebP to PNG makes it bigger; compressing a PNG does not change what it is. Choosing the wrong one is the most common reason a result disappoints.

2. 2

   Do the lossless pass first

   PNG, GIF and BMP have a route that changes no pixel values at all. Run it before you consider throwing anything away: it is free, and it tells you how much slack the file had.

3. 3

   Judge a lossy setting by the picture

   Look at the two images side by side at the same size and read the bytes underneath. Do not carry a quality number over from another tool — it does not mean the same thing there.

4. 4

   Resize before you re-encode

   Halving the width quarters the area, which is almost always a larger saving than any quality setting, and it costs nothing if the image was oversized for its slot to begin with.

5. 5

   Look at the files that came out bigger

   Some will: a JPEG already saved at high quality, a PNG already optimised, a small icon where format overhead dominates. Keep the originals for those. A tool that only ever reports savings is not measuring anything.

• You have a folder of images to shrink

  Image converter

  Unlimited batch with a per-file size delta, including when a conversion made a file larger.

• You want a PNG smaller with nothing changed

  Image compressor

  oxipng rewrites how the file is stored without touching a pixel value, which a canvas round-trip cannot do.

• You are shipping an SVG

  SVG optimiser

  Every setting that can break the file says what it costs, and a side-by-side preview shows whether it did.

• You have a logo as a PNG and need it as a vector

  PNG to SVG

  It traces in your browser, locks the output to exact hex colours, and shows the bytes, path count and per-pixel error of every result, with a warning when the image is a photo.

• You need an SVG as a PNG, for a screen or for print

  SVG to PNG

  It names the web fonts and linked images a browser would drop, embeds them if you drop the files in, and writes the ppi into the PNG.

• You are putting code on a slide or in a post

  Code to image

  An SVG of real, selectable text or a PNG at exact 2× or 3×, with every colour measured against its background, failing ones lifted with the hue kept, and alt text written.

• You need many photos at one size, a print size or under a KB limit

  Resize image

  Pixels, longest side, percent or centimetres at a ppi it writes into the file; portrait phone photos come out upright and in true colour, and each file can be held under a byte limit.

• You need one photo at every social platform’s size

  Social media image sizes

  Each size is taken from the platform’s own page and dated, cropped around one focal point, and checked against the upload limit.

• You are posting a screenshot of your product

  Screenshot beautifier

  A browser or device frame on a gradient, with the screenshot copied pixel for pixel at the density it was taken at, private details covered so they cannot be unblurred, and no metadata in the file.

• You need to crop, turn and resize the same picture

  Image editor

  All four transforms in one pass, so the image is not re-encoded three times on the way through.

• You are inlining a small asset

  Data URI converter

  It gives the encoded size and a verdict on whether inlining is the right call at that size.

• You need a size in another unit

  Pixel converter

  Pixels to inches, centimetres, points, rem and em, and it asks whether the pixels are for CSS, for print or for this screen, because the answer differs.

• Squoosh, the reference client-side compressor, has no batch mode at all; Caesium caps a session at ten files and TinyPNG’s web tool at twenty.

• A 21,493-byte flat graphic came out of a canvas PNG encode at 38,905 bytes — 81% larger — and out of oxipng at 3,350 bytes, losslessly.

• No browser can encode AVIF from a canvas, which is why it is not offered here — decode support is widely available and frequently confused with encode.

• Tracing a photograph makes it bigger, not smaller: a 39,044-byte WebP render traced to a 228,206-byte SVG, 5.8 times the size, with 636 paths (measured October 2026).

• Canvas dimensions are capped near 8192 pixels a side and about 16 megapixels in total on iOS before 2024; exceeding it returns a blank image rather than an error.

• Neither Chromium nor WebKit writes a resolution into the PNG it encodes from a canvas (measured October 2026), so a 300 ppi export opens in Photoshop at 72 unless the converter adds the pHYs chunk itself.

• Of the 65 syntax themes that ship with the shiki highlighter, 56 set at least one token colour under 4.5:1 on their own background, and 49 fail on the comment colour (measured October 2026).

• A Mac writes 144 ppi into a Retina screenshot, so a 1920 × 1200 capture is a 960 × 600 window at 2×; exported at 2×, it needs no scaling at all, yet shots.so’s “1x” export of its default layout was 1920 × 1440 whatever was placed in it (measured October 2026).

• Reference

  WebP to PNG

  Turn WebP into PNG when something downstream refuses it.

• Reference

  WebP to JPG

  WebP to JPEG, with the transparency question answered.

• Reference

  JFIF to PNG

  JFIF is a JPEG with a different extension. Here is the honest version.

• Reference

  PNG to JPG

  PNG to JPEG for photographs — and when not to.

• Reference

  PNG to WebP

  The conversion that actually makes files smaller.

• Reference

  Pixels to inches

  Pixels to inches and back, for CSS, for print, or as measured on your screen.

• Reference

  Pixels to centimetres

  Pixels to centimetres and millimetres, and back, with A-series paper in whole pixels.

• Reference

  Pixels to points

  Pixels to points and back: move a type size from a design file to a document.

• Reference

  Pixels to rem

  Pixels to rem and back, at your real root size, not just the assumed 16.

• Reference

  Pixels to em

  Pixels to em and back for a given parent size, with the compounding shown.

• 9 tools

  Colour

  Check it, fix it, extract it, turn it into a system.

• 4 tools

  CSS

  Gradients and surfaces as CSS you paste, measured as they will paint.

• 3 tools

  Typography

  Pairing, scale, readability and font identification — measured the same way.

• 3 tools

  Branding

  Marks, codes and sheets — the things that carry the brand.

• 6 tools

  Writing

  Resumes, cover letters, word counts and interface copy, held to the same standard as the pixels.

• 15 tools

  PDF

  Merge, split, protect and convert — none of it uploaded.

• 3 tools

  Video & audio

  Trim, extract and convert — decoded by your own browser, not a server.