What is the difference between DPI and PPI?

PPI (pixels per inch) measures the pixel density of a digital screen or image file — it is a property of the image. DPI (dots per inch) measures how many ink dots a printer places per inch — it is a property of the output device. A 300 PPI image file printed at 300 DPI produces a high-quality print. The two terms are often used interchangeably in casual conversation, but technically they refer to different things.

How many pixels do I need for a 4×6 print at 300 DPI?

A 4×6 inch print at 300 DPI requires an image that is at least 1200×1800 pixels (4 × 300 = 1200 pixels wide, 6 × 300 = 1800 pixels tall). This is 2.16 megapixels — well within the capability of any smartphone camera made after 2015.

What PPI is Apple Retina display?

Apple defines Retina as the point where individual pixels are indistinguishable at a typical viewing distance. For iPhones held about 12 inches away, Apple sets the Retina threshold at 300 PPI. The iPhone 15 has a 460 PPI Super Retina XDR display. For MacBook laptops (held farther away), the Retina threshold is around 220 PPI. For desktop iMacs (24-inch, 4.5K), the display is 218 PPI.

DPI vs PPI: Pixel Density Guide for Screens and Print

DPI and PPI Defined

PPI (pixels per inch) is the density of pixels in a digital image or on a screen. It is calculated as: PPI = √(width² + height²) ÷ diagonal inches. A higher PPI means finer detail.

DPI (dots per inch) refers to the physical output resolution of a printer — how many separate ink drops it lays down per inch. Modern inkjet printers produce 300–2400 DPI; laser printers typically 600–1200 DPI. When you export a photo "at 300 DPI" from editing software, you are really setting its PPI metadata so that the printer knows how large to print it without scaling.

Print Resolution Standards

Higher PPI is not always necessary. The table below shows common output quality thresholds for digital images destined for print.

PPI	Quality Level	Typical Use
72 PPI	Screen / web only	Websites, email, social media
96 PPI	Screen standard	Windows display default
150 PPI	Acceptable print	Posters, banners, large-format
300 PPI	Photo-quality print	4×6, 8×10, fine art prints
600 PPI	Ultra-fine print	Line art, technical drawings

Pixel Dimensions Needed for Common Print Sizes at 300 DPI

Multiply each dimension in inches by 300 to get the required pixel count. The examples below reflect exact 300 DPI requirements.

Print Size (inches)	Pixels Required (300 DPI)	Approximate Megapixels
4 × 6 in	1200 × 1800 px	2.2 MP
5 × 7 in	1500 × 2100 px	3.1 MP
8 × 10 in	2400 × 3000 px	7.2 MP
11 × 14 in	3300 × 4200 px	13.9 MP
16 × 20 in	4800 × 6000 px	28.8 MP
24 × 36 in	7200 × 10800 px	77.8 MP

Smartphone PPI Comparison

Modern flagship phones push PPI well beyond what the human eye can resolve at arm's length (roughly 300 PPI threshold). Higher PPI still benefits text clarity and fine details in photos.

Device	Resolution	Screen Size	PPI
iPhone 15 Pro	2556 × 1179	6.1 in	460 PPI
Samsung Galaxy S24	2340 × 1080	6.2 in	416 PPI
Google Pixel 8	2400 × 1080	6.2 in	428 PPI
Standard HD Phone	1280 × 720	5.5 in	267 PPI
Budget Android	1600 × 720	6.5 in	270 PPI

Scaling for Retina and HiDPI Displays

Operating systems on high-PPI screens use a display scale factor (2× on Retina, 1.5× on many Windows HiDPI screens). A 2× Retina display renders everything at double the pixel count internally but presents it at the logical size of a 1× screen. Web images should be served at 2× size for Retina screens to avoid blurriness — a 200 px wide image on a Retina site should be 400 px wide in the source file.

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