How to Check Photo Size in mm?

Unfortunately, directly checking the photo size in millimeters (mm) isn't a standard feature readily available in most operating systems or image viewers. Photo size is usually displayed in pixels, bytes (KB, MB), or dimensions (width and height). To find the equivalent size in millimeters, you'll need to know the DPI (dots per inch) or PPI (pixels per inch) of the image when printed or displayed. Here's a breakdown:

Understanding the Relationship Between Pixels, DPI/PPI, and Millimeters

• Pixels: The fundamental unit of digital images. They define the width and height.
• DPI/PPI: DPI (dots per inch) refers to the resolution of a printed image, while PPI (pixels per inch) refers to the resolution on a screen. They indicate how many pixels are packed into each inch.
• Millimeters: A unit of physical length.

Steps to Determine Photo Size in mm (Indirectly)

1. Determine the DPI/PPI: This is crucial. The DPI/PPI value tells you how many pixels will be printed or displayed per inch. This information is often linked with the image in its metadata, especially if the image has been prepared for printing. Sometimes, you might need to assume a standard DPI (like 300 DPI for high-quality prints, or 72 DPI for web images) if it's not explicitly stated.

2. Find the Pixel Dimensions:

   • Windows: Right-click the image file, select "Properties," go to the "Details" tab, and find the "Dimensions" (e.g., 1200 x 1800 pixels).
   • macOS: Right-click (or two-finger tap) the image file, select "Get Info," and find the "Dimensions."
   • Android: Open the photo in Google Photos, tap the three dots in the top right corner, and scroll down to see "Image size." The dimensions will be listed there.

3. Calculate the Size in Inches: Divide the pixel dimensions by the DPI/PPI.

   • Example: If your image is 1200 x 1800 pixels and the DPI is 300, then:
     • Width: 1200 pixels / 300 DPI = 4 inches
     • Height: 1800 pixels / 300 DPI = 6 inches

4. Convert Inches to Millimeters: Multiply the size in inches by 25.4 (since 1 inch = 25.4 mm).

   • Example (Continuing from above):
     • Width: 4 inches * 25.4 mm/inch = 101.6 mm
     • Height: 6 inches * 25.4 mm/inch = 152.4 mm

   Therefore, the image would be approximately 101.6 mm x 152.4 mm when printed at 300 DPI.

Summary

While operating systems don't directly display photo size in mm, you can calculate it by:

1. Finding the pixel dimensions of the image.
2. Knowing (or assuming) the DPI/PPI.
3. Dividing the pixel dimensions by the DPI/PPI to get the size in inches.
4. Multiplying the size in inches by 25.4 to get the size in millimeters.