PNG

Convert PNG to 300 DPI

Fix PNG DPI metadata without re-encoding. Updates the pHYs chunk while keeping transparency and pixel data intact. Secure Processed locally — your files never leave your device.

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Batch processing supported

DPI

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How PNG DPI Works

PNG files store physical pixel density in an optional chunk called pHYs (physical pixel dimensions). This chunk holds the pixel-per-unit values for X and Y axes, plus a unit identifier (1 = meter).

To store 300 DPI in a PNG, we convert: 300 ÷ 0.0254 = 11,811 pixels per meter. That number is written as a 4-byte big-endian integer into the pHYs chunk. We also recalculate the CRC checksum so the file remains valid.

If no pHYs chunk exists, we insert one before the first IDAT chunk. The PNG spec requires this ordering.

PNG vs JPEG for Printing

PNG supports transparency (alpha channel), which makes it essential for logos, stickers, and overlays. When printing:

Note about transparency: Some print shops flatten transparency to white when printing PNGs. Always check your print service's spec before submitting.

Frequently Asked Questions

Will setting 300 DPI change how my PNG looks?

No. PNG is a lossless format and this tool only touches a small metadata chunk. Every pixel is preserved exactly.

Where is DPI stored in a PNG?

In a chunk called pHYs, which records pixels per metre rather than per inch. The tool writes that chunk with the right value and a correct CRC checksum, adding it if the file has none.

Why does my PNG show no DPI at all?

Most software that exports PNGs omits the pHYs chunk entirely, which is perfectly legal. Programs then assume a default, usually 72, when deciding what physical size to give the image.

My print shop still rejects the file. What now?

The pixel count is probably the real problem. Multiply the printed width in inches by 300 to find the minimum you need. If the file falls short, reproduce it smaller or recreate it at a higher resolution.

How many pixels do I need for a given print size?

Multiply each side in inches by 300. A 5 by 7 print needs 1,500 by 2,100 pixels, and an A4 page at 8.27 by 11.69 inches needs about 2,480 by 3,508.