25.08.13
Does This Image Have Enough Resolution for Printing? A Simple Calculation Gives You the Answer.
Hachiware 
Mikeneko Hachiware You Can Tell from the Pixels Whether an Image Meets the Required Print Resolution
Whether an image meets the required print resolution depends on
the image’s pixel count and the actual print size.
The actual print size and the required resolution
By calculating with these two factors, you get the answer (required pixel count).
To deepen your understanding of resolution, I recommend trying this calculation at least once.
Let’s walk through the steps together.
1. Check the Required Resolution for This Print Job
The bicolor cat above is trying to print a full-color A3 poster.
After checking with the print shop, they found that a resolution of 350 ppi is required.
2. Check the Actual Print Size of the Image
Even though the image is for an A3 poster, it won’t fill the entire A3 sheet —
it’s planned to be used in just a portion of the poster.
The actual size of this portion is W20 × H10 cm.
3. Convert the Size to Inches
Since the calculation uses inches, we need to convert from cm to inches.
Divide the actual size (cm) by 1 inch (2.54 cm).
10 cm ÷ 2.54 = approximately 3.94 inches
The actual size of this portion is W20 × H10 cm.
4. Calculate the Required Pixel Count
Multiply the actual size (in inches) by the required resolution.Resolution (ppi) indicates how many pixels are lined up in one inch.
In this case, since a resolution of 350 ppi is required,
multiply the actual size (in inches) calculated earlier by 350 to find the required pixel count.
3.94 inches (actual print size) × 350 ppi (required resolution) = 1,379 pixels
In other words, if the image is 2,754 × 1,379 pixels or larger, it meets the required resolution.
Hachiware Summary
You can check if an image meets the required print resolution with this calculation:
(Finished size in cm ÷ 2.54 cm) × Required resolution = Required pixel count
Deepen Your Understanding with the Reverse Calculation
To deepen your understanding, let’s now calculate what the resolution would be if you used the image as-is.
Divide the pixel count by the size.4,000 pixels ÷ 7.87 inches = approximately 508 ppi
2,000 pixels ÷ 3.94 inches = approximately 508 ppi
Hachiware What happens when the image’s aspect ratio differs from the print size ratio?
In the example above, the aspect ratios are the same, so both horizontal and vertical resolutions are 508 ppi. However, when they differ, the values change.
Example: If the bicolor cat’s image were 4,000 × 3,000 px
4,000 pixels ÷ 7.87 inches = approximately 508 ppi
3,000 pixels ÷ 3.94 inches = approximately 762 ppi
Even in this case, the correct answer is 508 ppi.
If you calculate based on the height of 3.94 inches, a 4:3 ratio image would fall short of the 7.87-inch width.
The idea is to use the width of 7.87 inches as the reference and crop the excess from the 3.94-inch height.
