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A3 Print (297×420 mm)

3508×4961 px @ 300 DPI

Print resolution differs from screen resolution by an order of magnitude — print needs 300 DPI or higher for the dot pattern to disappear, where a screen reads 72-96 DPI. A3 Print (297×420 mm) bakes the correct DPI into the file metadata so a print shop opens the image at the intended physical size — 11.7×16.5 inches (29.7×42.0 cm) — not at the screen-pixel size. The preset outputs 3508×4961 JPEG @ 300 DPI, which is the resolution required to land that physical size at print quality. Bring the file to a print shop, an inkjet, or a photo-print kiosk; the embedded DPI tells the renderer the intended page measurement so the printer's auto-fit doesn't guess wrong.

Specifications

Output dimensions	3508×4961 pixels
Aspect ratio	297:420 (297:420)
Resolution	300 DPI
Output format	JPEG @ 92% quality
Processing	100% in your browser — no upload
Cost	Free, unlimited

When you'd run A3 Print (297×420 mm)

Sending a 11.7×16.5 inch print order to an online photo lab.
Printing wallet-size or framed photos at a self-service kiosk.
Preparing trade-show, conference, or in-store collateral at the exact physical size.
Producing greeting cards, invitations, or thank-you cards from a digital design.

How A3 Print (297×420 mm) runs

This preset is a deterministic recipe — every step has fixed parameters so the result is byte-identical across runs of the same input.

Crop the image to a 297:420 aspect ratio. Mochi keeps the centre of the frame in the middle of the crop by default — drag the crop box if you want to recompose.
Resize to 3508×4961 px at 300 DPI as JPEG at quality 92%.

Where the work happens

A3 Print (297×420 mm) crops your input to 297:420 and resizes it to 3508×4961 px as JPEG — a 17.4-megapixel output. The work runs through canvas APIs and a WebAssembly image-encoder; the source image is decoded into an off-screen canvas, transformed in place, and re-encoded without any network upload.

Print pipelines read the embedded DPI metadata to set the page measurement; baking the right DPI before sending avoids the printer's auto-fit guessing wrong. The browser-side path also means the file never leaves your device — relevant when the input contains personally identifiable information, screenshots of private documents, ID scans, or proprietary product photography.

Common mistakes

Sending a 72-DPI screen file to print. The file may have the right pixel count but at 72 DPI it prints at 48.7×68.9 inches instead of the intended 11.7×16.5 inches. This preset bakes 300 DPI into the file metadata so the print renderer reads the correct page measurement.
Forgetting bleed margin. Most printers want 3 mm of bleed beyond the trim line. A3 Print (297×420 mm) outputs an exact 11.7×16.5 inch image — measure the bleed into your source before running, or expect the printer to crop into your composition.
Using sRGB for offset print. Some commercial print shops require CMYK at the 11.7×16.5 inch size; sRGB renders with a slight colour shift. Confirm the print shop's colour-profile expectation before sending.
Submitting a smaller-than-3508×4961 source. The preset upscales to fill 3508×4961 px, which softens fine detail. For 11.7×16.5 inch prints, start from a source at least that pixel size for best print sharpness.
Uploading sensitive images to a server-side tool. This preset runs entirely in your browser; the file never leaves your device. Verify this in your browser's network panel if working with confidential material.

FAQ

What does A3 Print (297×420 mm) output?

3508×4961 px at 300 DPI, saved as JPEG at quality 92%.

Why crop to 297:420?

The target platform — see the cited spec — uses 297:420 as its native frame. Submitting any other ratio means the platform's own crop runs, which often clips faces or text near the edge.

Why 300 DPI?

300 DPI is the print-grade resolution at which the dot pattern disappears at normal reading distance. Government photo offices, commercial print shops, and biometric scanners all assume 300 DPI; anything lower prints visibly soft.

Why JPEG and not PNG?

The target accepts JPEG, and JPEG compresses photographic content 5-10× smaller than PNG with no visible difference at quality 92%. PNG is the right choice only when the image has hard edges or transparency — which photo-ID, social posts, and product photos don't.

Does my image get uploaded?

No. This preset runs entirely in your browser using WebAssembly + canvas APIs — no server round-trip. You can verify this in your browser's network panel: only static asset requests, no image upload. The file never leaves your device.

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