Image File Size Calculator

How is Image Size Calculated?

A digital image is essentially a grid of colored dots (pixels). The file size depends on how many dots you have, and how much information you store for each dot.

The uncompressed file size formula is straightforward:

• Width × Height: The total number of pixels.
• Bit Depth: How many bits of color info per pixel.
• ÷ 8: Converts Bits into Bytes (since 8 bits = 1 Byte).

Understanding Bit Depth (Color)

The file size explodes as you add more colors. Here are the standards:

• 1-Bit (Monochrome): Only Black or White. Tiny file sizes.
• 8-Bit (Grayscale/GIF): 256 colors. Good for logos or icons.
• 24-Bit (True Color RGB): The web standard. Uses 8 bits for Red, 8 for Green, 8 for Blue. (8+8+8=24). Capable of 16.7 million colors.
• 32-Bit (RGBA): Adds an 8-bit "Alpha" channel for transparency. Used in PNGs.

The Compression Factor: JPEG vs. PNG

The formula above gives the Raw / Uncompressed size. If you saved a 20MP photo as a Raw Bitmap (BMP), it would be huge (60MB). To save space, we compress images.

Lossless Compression (PNG, TIFF)

Reduces file size without losing quality. It works like a ZIP file. It looks for patterns (like a big patch of blue sky) and writes "100 blue pixels" instead of "blue, blue, blue..."
Typical Ratio: 2:1 (File becomes 50% smaller).

Lossy Compression (JPEG)

This method deletes information that the human eye barely notices. It approximates colors.
Typical Ratio: 10:1 (File becomes 90% smaller!).

Calculating Print Size

Knowing the pixel dimensions also tells you how big you can print the image without it looking blurry. Standard print quality is 300 DPI (Dots Per Inch).

To find the max print size: Divide Width by 300.

Example: 3000px width ÷ 300 = 10 inches wide.