Megapixel Calculator

Megapixel and image resolution calculations help photographers determine print size limits, file sizes, crop factors, and display suitability. A megapixel (MP) is one million pixels. Resolution is expressed as width × height in pixels, and the megapixel count is simply that product divided by one million.

Megapixel count formula: Megapixels = (Width in pixels × Height in pixels) ÷ 1,000,000

Maximum print size formula (at given DPI): Print Width (inches) = Image Width (pixels) ÷ DPI Print Height (inches) = Image Height (pixels) ÷ DPI

Where:

• DPI = Dots Per Inch (printing resolution)
  • 300 DPI: professional print quality (minimum for sharp prints)
  • 240 DPI: very good print quality (most people can’t see difference from 300)
  • 150 DPI: acceptable viewing at arm’s length
  • 72 DPI: screen resolution only — blurry when printed

File size formula (uncompressed): File Size (MB) = (Width × Height × Bit Depth ÷ 8) ÷ 1,048,576

• 24-bit color = 3 bytes per pixel (8 bits × 3 channels: red, green, blue)
• 48-bit color (RAW) = 6 bytes per pixel

JPEG compression: Typically reduces file size by 10–25× vs. uncompressed RAW files: Approximately 1.0–1.5× the uncompressed size after lossless compression

Megapixel benchmarks by use case:

• Social media: 2–4 MP sufficient
• Large poster print (24"×36" at 150 DPI): 23 MP minimum
• Billboard (viewed from 10+ feet): 2–5 MP sufficient
• Magazine full-page (8.5"×11" at 300 DPI): 8.5 MP minimum
• Fine art large-format print: 50+ MP preferred

Worked example: Camera shoots 6000 × 4000 pixel images.

• Megapixels: 6000 × 4000 ÷ 1,000,000 = 24 MP
• Maximum print at 300 DPI: 6000÷300 × 4000÷300 = 20 inches × 13.3 inches — excellent for framed prints
• Maximum print at 150 DPI: 40 inches × 26.7 inches — suitable for canvas prints viewed at normal distance
• Uncompressed file size: 6000 × 4000 × 3 ÷ 1,048,576 = 68.7 MB per image
• JPEG at quality 90: approximately 8–12 MB per image