What is this calculator?
Converts an image between JPEG, PNG, and WebP entirely in your browser. It first validates the conversion and shows you exactly what will happen — output format, quality, file name, and how transparency and metadata will be treated — before the encode runs.
Use it when:
- You need an image in a specific format for a system that only accepts that format.
- You want to compare the three formats for the same picture.
- You would rather not upload a private image to an online converter.
Intended for: Anyone converting images for the web, for a document, or for an upload requirement.
How is this calculated?
- The file you choose is read only for its type and name — nothing is uploaded, and the image itself never leaves your device.
- The tool validates that the source format is supported and that the requested output format and quality are valid together, producing a deterministic conversion plan: output format, quality, output file name, and the transparency and metadata policies that will apply.
- The output file name is derived from the source name with its extension replaced, so the result is predictable rather than randomly named.
- Your browser then decodes the image, draws it to a canvas at its original dimensions, and re-encodes it in the target format using its own built-in encoder.
- Because the image is decoded to raw pixels and re-encoded, the output carries only pixel data — embedded metadata such as EXIF is not preserved.
Example
Converting `holiday-photo.png` to WebP at quality 0.92.
- The plan validates PNG as a supported source and WebP as a supported target.
- The output name becomes `holiday-photo.webp`.
- PNG transparency is preserved, because WebP supports an alpha channel.
Result: `holiday-photo.webp` at quality 0.92, transparency preserved, metadata not carried over.
Frequently asked questions
Which format should I choose?
WebP for the web: it is smaller than both JPEG and PNG at comparable quality and supports transparency. JPEG for photographs where maximum compatibility matters. PNG for screenshots, logos, and anything with sharp edges or transparency that must stay lossless.
What does the quality setting actually do?
It controls how aggressively a lossy encoder discards detail. Values around 0.8 to 0.92 are usually indistinguishable from the original at a fraction of the size; below about 0.7, compression artefacts become visible around edges and in flat areas.
What happens to transparency?
PNG and WebP both support an alpha channel, so transparency survives between them. JPEG does not, so transparent pixels are composited onto a white background when converting to JPEG.
Is my image uploaded anywhere?
No. The image is decoded and re-encoded by your own browser. It is never transmitted to a server, and nothing is stored after you leave the page.
Assumptions
What this calculator takes as given:
- Conversion happens entirely in your browser; the image is never uploaded to or stored on a server.
- Pixel dimensions are preserved exactly — the tool changes the format, not the size.
- The quality setting applies only to lossy encoders (JPEG and WebP); PNG is always lossless.
- Encoding uses your browser's own image encoder, so the exact output bytes can differ slightly between browsers.
Limitations
What this calculator cannot know or does not model:
- Metadata such as EXIF, GPS coordinates, and colour profiles is not carried over — useful for privacy, but a loss if you needed it.
- Resizing, cropping, rotation, and other edits are outside the tool's scope.
- Animated images are converted as a single still frame.
- Very large images may exhaust browser memory, since decoding happens in the page.
- The final file size depends on your browser's encoder and cannot be predicted before encoding.