DPI vs PPI: Resolution Explained

The Confusion

DPI and PPI are often used interchangeably, but they're actually different concepts. Understanding the distinction is essential for anyone working with digital or print images.

Quick answer:

• PPI (Pixels Per Inch): Resolution of a digital image or screen
• DPI (Dots Per Inch): Resolution of a printed image

What is PPI?

PPI (Pixels Per Inch) measures how many pixels are displayed in one inch of a digital image or screen.

Digital Images

When you open an image on your computer, its PPI setting determines how large it appears when printed at its native size, but it doesn't affect how it looks on screen.

Example: A 3000×2000 pixel image can have any PPI setting:

• At 300 PPI: prints at 10×6.67 inches (3000÷300 = 10)
• At 150 PPI: prints at 20×13.33 inches (3000÷150 = 20)
• At 72 PPI: prints at 41.67×27.78 inches (3000÷72 = 41.67)

The pixel dimensions stay the same—only the intended print size changes.

Screen Displays

Screen PPI is determined by the physical screen size and resolution:

• Standard screens: ~96 PPI
• Retina/High-DPI screens: 200-400+ PPI
• Smartphone screens: 300-500+ PPI

Higher PPI screens display sharper images because they pack more pixels into each inch.

What is DPI?

DPI (Dots Per Inch) measures how many ink dots a printer can place in one inch. This is a physical printer capability.

Printer Resolution

Printers create images by placing tiny dots of ink on paper. DPI measures the printer's ability to place these dots:

• Basic printers: 300-600 DPI
• Photo printers: 1200-4800 DPI
• Professional printers: 2400-5760 DPI

DPI vs. Image Quality

Higher printer DPI doesn't always mean better results. What matters is matching your image PPI to the printer's capabilities:

• A 300 PPI image on a 1200 DPI printer will look excellent
• A 72 PPI image on a 2400 DPI printer will look pixelated
• The printer uses multiple dots to create each pixel

Key Differences

Resolution Standards

For Print

• 300 PPI: Standard for high-quality photo printing and professional work
• 150 PPI: Acceptable for large posters viewed from a distance
• 72 PPI: Too low for printing (will appear pixelated)

For Web/Screen

• PPI doesn't matter for web: Only pixel dimensions matter (e.g., 1920×1080)
• File metadata: Web images often have 72 PPI metadata, but this is meaningless for display
• What matters: Total pixel count and file size

Why 72 PPI for Web?

You'll often see web images set to 72 PPI. This is a historical convention from old Mac displays that had 72 pixels per inch. Modern screens vary widely (96-500+ PPI), so this setting is meaningless for web images. Browsers ignore PPI metadata and display images based on pixel dimensions only.

Calculating Print Size

To determine how large an image will print at a given PPI:

Example 1: Standard Photo Print

Image: 3000×2000 pixels at 300 PPI

• Width: 3000 ÷ 300 = 10 inches
• Height: 2000 ÷ 300 = 6.67 inches
• Result: High-quality 10×6.67" print

Example 2: Large Poster

Image: 3000×2000 pixels at 150 PPI

• Width: 3000 ÷ 150 = 20 inches
• Height: 2000 ÷ 150 = 13.33 inches
• Result: 20×13.33" poster (acceptable quality for viewing distance)

Calculating Required Pixels

To determine the pixel dimensions needed for a specific print size:

Example: 8×10" Photo Print

Target: 8×10 inches at 300 PPI

• Width: 8 × 300 = 2400 pixels
• Height: 10 × 300 = 3000 pixels
• Result: Need a 2400×3000 pixel image

Changing PPI Without Resampling

You can change an image's PPI setting without changing its pixel dimensions. This only affects the intended print size, not the image data:

In Photoshop

1. Image → Image Size
2. Uncheck "Resample"
3. Change Resolution (PPI)
4. Notice width/height in inches changes, but pixels stay the same

Why Do This?

Setting the correct PPI helps design software and print services understand your intended print size, but it doesn't change the actual image data.

Resampling vs. Resizing

Resizing (Changing PPI Only)

• Changes intended print dimensions
• Keeps pixel dimensions the same
• No quality loss
• File size unchanged

Resampling (Changing Pixel Dimensions)

• Adds or removes pixels
• Changes image data
• Upsampling (enlarging) reduces quality
• Downsampling (reducing) can improve print quality if starting oversized

Common Scenarios

Scenario 1: Web to Print

Problem: You downloaded an image from a website and want to print it.

Solution:

1. Check pixel dimensions (e.g., 1920×1080)
2. Calculate print size at 300 PPI: 1920÷300 = 6.4 inches wide
3. If too small, you need a higher resolution image or accept lower quality
4. Don't upscale—it won't add real detail

Scenario 2: Phone Photo to Print

Problem: Can your 12MP phone photo (4000×3000 pixels) make a quality print?

Solution:

• At 300 PPI: 4000÷300 = 13.3" × 10" — Excellent quality
• At 150 PPI: 4000÷150 = 26.7" × 20" — Good for posters
• Yes! Modern phone cameras have enough resolution for most prints

Scenario 3: Screen Capture to Documentation

Problem: You took a screenshot at 1920×1080 for a printed manual.

Solution:

• At 300 PPI: Only 6.4×3.6 inches
• At 150 PPI: 12.8×7.2 inches (better for documentation)
• Consider taking screenshots on a high-DPI display for more pixels

Best Practices

• For web: Ignore PPI, focus on pixel dimensions and file size
• For print: Use 300 PPI for photos, 150 PPI for large posters
• Never upscale: If you don't have enough pixels, print smaller or accept lower quality
• Save originals: Keep high-resolution originals, create web versions separately
• Check before cropping: Ensure you'll have enough pixels left for your intended print size
• Design at final size: When creating graphics, design at the final pixel dimensions needed

Tools and Resources

• Image Resizer - Change dimensions while maintaining quality
• Image Optimization Guide - Prepare images for web
• Image File Formats - Choose the right format for print vs. web

Quick Reference