Image Resolution for Printing: Pixel Size Chart

For photos and documents viewed at close range, 300 ppi is a practical starting point for print preparation. It is not a universal requirement: the print process, paper, viewing distance, and your printer's specifications all matter. Always follow the print provider's requirements when they differ from a general guideline.

This guide gives you a quick pixel-size chart, the formula behind it, and a reliable workflow for checking an image before printing. It also explains why changing a resolution field to “300 dpi” does not automatically add detail.

Quick pixel chart for common print sizes

The values below are rounded up to avoid falling short. If the artwork needs bleed, calculate from the dimensions including bleed rather than the final trimmed size.

An A4 image covering the full page at 300 ppi therefore needs about 2,481 × 3,508 pixels. If you will crop the image, start with a larger file so the pixels discarded by the crop do not leave the final placement undersized.

How to calculate the required pixels

Use this formula when the print dimensions are in millimeters:

Required pixels = print size in mm ÷ 25.4 × ppi

For the 210mm short edge of A4, 210 ÷ 25.4 × 300 = 2,480.31..., which rounds up to 2,481 pixels.

To calculate the effective resolution of an existing image, reverse the formula:

Effective ppi = image pixels ÷ print size in inches

For example, placing a 1,200-pixel-wide image across the 210mm short edge of A4 produces only about 145 ppi. Changing the file's resolution metadata to 300 ppi does not change that result unless the actual pixel dimensions also change.

PPI and DPI are not the same measurement

• PPI (pixels per inch) describes how densely an image's pixels are placed on the printed page.
• DPI (dots per inch) describes the physical dots produced by a printer.

Print instructions sometimes use “300 dpi image” as shorthand, but image resolution is technically measured in ppi. A printer's output dpi does not need to equal the image's ppi.

A dependable prepress workflow

1. Decide the placed size

Calculate from the size of the image on the page, not automatically from the paper size. An image placed 100mm wide on an A4 page only needs to satisfy the requirements for that 100mm placement.

2. Check the printer's specification

Use the provider's required ppi, color mode, file format, and bleed. Requirements may differ for color photographs, grayscale images, and monochrome line art.

3. Check the source pixel dimensions

Windows file properties and macOS Finder or Preview can show an image's width and height in pixels. In Photoshop, Image Size shows the relationship between pixel dimensions, print dimensions, and resolution.

4. Check effective resolution after placement

Enlarging a raster image in Illustrator or layout software reduces its effective ppi. A 300 ppi image enlarged to 200% becomes approximately 150 ppi at its placed size. Reducing it to 50% makes the effective density approximately 600 ppi.

What to do when an image is too small

Print it smaller

This is the most reliable option. Reducing the placed dimensions increases the number of available pixels per inch without inventing new image data.

Find the original file

Images downloaded from email, messaging apps, or social media may have been compressed. Look for the camera original, the working PSD, or a higher-resolution version from the original asset source.

Upscale only as much as needed

When a larger source is unavailable, AI enlargement can add pixels and make edges or visible detail easier to inspect at the target size. You can enlarge an image by 2× or 4× with Kogashitsuka AI.

AI-generated detail is not a perfect recovery of information that was absent from the source. Check faces, labels, small text, diagrams, and product details at 100%, then make a proof print when accuracy matters.

Account for viewing distance

Posters and large displays are viewed differently from handheld prints. A value below 300 ppi may be acceptable at a normal viewing distance. Evaluate the real use case, not the number alone.

Common mistakes

Changing 72 to 300 without adding pixels

With resampling disabled, changing the resolution value changes the printed dimensions but leaves the pixel count unchanged. A field displaying 300 ppi does not prove the image has enough pixels for the intended size.

Repeatedly saving a small JPEG

JPEG can be recompressed with each save. Keep a lossless working file such as PSD or TIFF, and export the delivery JPEG once at the end.

Judging only from the screen

A monitor cannot fully reproduce physical size, paper, ink, or the printer's output. For important work, inspect at 100% and make a proof at the intended dimensions.

Final print-image checklist

• Confirmed trim size and bleed
• Followed the printer's ppi, color, and file requirements
• Retained enough pixels after cropping
• Checked effective resolution at the placed size
• Inspected AI-enhanced faces, text, and edges
• Avoided unnecessary JPEG saves and downsampling
• Made a full-size proof when detail or color is critical

Frequently asked questions

Is 300 ppi always required for printing?

No. It is a useful standard for high-quality work viewed up close, but large-format output can use a lower value depending on viewing distance and the print process. Follow the provider's specification.

Is a 4K image enough for A4?

“4K” does not define the aspect ratio. A 3,840 × 2,160 image has enough horizontal pixels for landscape A4, but it does not match the page shape and may require cropping. Judge the pixels that remain in the final crop.

Does converting an image to 300 dpi improve quality?

Changing metadata alone does not improve it. Compare the actual pixel dimensions with the intended print size, then obtain a larger source or resample only when necessary.

Summary

Print resolution depends on three concrete values: the image's pixel dimensions, its physical size on the page, and the target ppi. Start with 300 ppi for close-viewed print work, then adapt to the printer's requirements and viewing conditions.

If the source is too small, first reduce the print size or find a larger original. When neither is possible, use 2× or 4× AI enlargement and inspect the output carefully before placing it in the final artwork.

References

• Adobe Photoshop: Resolution specs for printing images
• Adobe Photoshop: Printed image resolution