Image Resolution Calculator

Computes total pixel count, megapixel rating, estimated uncompressed file size, and maximum print dimensions at a target DPI from a width and height. File-size estimates assume 24-bit color depth unless specified otherwise.

Print dimensions follow the standard rule: pixels divided by DPI. A 6000×4000 image (24 MP) prints at roughly 20×13.3 inches at 300 DPI without upscaling. Aspect ratio and orientation are preserved across all derived measurements.

The mathematical basis is straightforward. Total pixels equals width × height. Megapixels equals total pixels divided by one million. Uncompressed file size at 24-bit color (8 bits per channel × 3 channels) equals total pixels × 3 bytes. A 24 MP image therefore occupies 72 MB uncompressed — a number that surprises photographers used to 8 MB JPEG files because compression typically reduces size by an order of magnitude.

DPI (dots per inch) determines print fidelity. The 300 DPI standard for photo printing originates from the resolution at which most humans cannot distinguish individual dots at typical viewing distance (10–14 inches). At 150 DPI, dots become visible to careful observers; at 75 DPI, they are obvious. Large-format work compensates with viewing distance: a billboard viewed from 50 feet does not require the resolution of a 4×6 print held in the hand.

A worked example for a Sony A7R V (61 MP, 9504×6336 native): the file occupies 181 MB uncompressed in 24-bit color, 240 MB in 16-bit-per-channel. At 300 DPI it prints 31.7×21.1 inches without resampling. At 240 DPI (the threshold for inkjet output where individual droplets blur into continuous tone) it prints 39.6×26.4 inches. At 150 DPI for a banner it prints 63.4×42.2 inches. Beyond that, upsampling becomes necessary and the perceived sharpness depends on the upscaling algorithm.

Limitations: the calculator assumes lossless rendering. Real-world prints are bottlenecked by paper, ink, and printer driver resampling. A 12 MP image printed at 8×10 on glossy photo paper at 300 DPI typically looks identical to a 24 MP image at the same size because lens diffraction, paper texture, and ink dot gain dominate. Megapixel count above the lens's resolving power is wasted. Phone-sensor megapixels are particularly suspect; a 108 MP phone image binned down to 27 MP usually produces a sharper print than the full-resolution capture.