The 4x6 Photo Print size (1200×1800px)
The 4x6 inch print is the most common photo size in the world, and at 300 DPI it measures exactly 1200 by 1800 pixels. Its 2:3 aspect ratio is the same shape most DSLR and mirrorless cameras capture natively, which is why a 4x6 usually prints your photo with little or no cropping, unlike square or 8x10 formats that trim the frame. If you shoot on a standard camera, this is the size that respects your original composition.
Sizing to 1200x1800 means your image maps perfectly onto a 4x6 sheet at the resolution photo labs and home photo printers expect. At 300 dots per inch the print holds fine detail, skin tones, and texture without looking soft, which is the whole point of a physical keepsake. Because 4x6 is inexpensive and universal, it is the default for photo albums, frames, and mailers, and matching its exact proportions avoids the white borders or auto-crop that appear when a mismatched image is forced onto the paper.
One thing to watch is borderless printing, where labs enlarge the image slightly and trim the edges, so keep faces and important elements a little away from the very edge of the frame. If your source is a different ratio, resizing to a strict 2:3 may crop some content, so preview the framing first. Everything here resizes 100% in your browser with no upload and for free, so your memories stay private on your device. Lab requirements vary, so confirm ratio, DPI, and border settings before a large order.