Pixel Ratio Calculator
The Pixel Ratio Calculator converts between CSS pixels and physical (device) pixels using the device pixel ratio (DPR). Calculate the actual rendered resolution on Retina and HiDPI displays, and determine optimal image sizes for crisp rendering.
🕐 Recent Calculations
What is Pixel Ratio?
Device pixel ratio (DPR) is the ratio of physical pixels to CSS pixels on a display. A DPR of 2 (Retina) means each CSS pixel is rendered using a 2×2 grid of physical pixels. A 375×812 CSS viewport on an iPhone at 3× DPR actually renders 1125×2436 physical pixels.
Understanding DPR is essential for web developers to serve appropriately sized images. A 200×200 CSS image needs a 400×400 source file for 2× displays and 600×600 for 3× displays to appear crisp. Without accounting for DPR, images appear blurry on high-density screens.
Formulas & Equations Used
This Pixel Ratio Calculator uses the following core equations:
1 Physical Pixels from CSS ▼
A 375px CSS width at 3× DPR: Physical = 375 × 3 = 1125 physical pixels.
2 CSS Pixels from Physical ▼
A 2560×1440 display at 2× DPR renders as 1280×720 CSS pixels.
3 Image Size for Target DPR ▼
A 300×200 CSS image area needs 600×400 source for 2× DPR, 900×600 for 3× DPR.
How to Use This Pixel Ratio Calculator
Follow these 3 simple steps:
Enter Your Values
Type the known values into the input fields above. The Pixel Ratio Calculator accepts any positive numbers.
Choose Calculation Mode
Select Solve, Simplify, or Scale mode in the calculator. Each applies different equations to your inputs.
View Results
Click Calculate to see your answer with a visual ratio bar, pie chart, and step-by-step solution breakdown.
Example Problems & Step-by-Step Solutions
Here are 3 worked examples using this Pixel Ratio Calculator:
Example 1 iPhone 14 Pro: 393×852 CSS at 3× DPR
Example 2 Image for 2× and 3× displays
Example 3 Calculate DPR from screen specs
Frequently Asked Questions
What is device pixel ratio (DPR)? ▼
DPR is the ratio between physical display pixels and CSS (logical) pixels. DPR 1 = standard displays. DPR 2 = Retina/HiDPI (Apple, many laptops). DPR 3 = high-end phones (iPhones, Samsung flagships).
How do I find my screen's pixel ratio? ▼
In a browser, open the console and type window.devicePixelRatio. Common values: 1 (standard monitors), 1.25 or 1.5 (Windows scaling), 2 (MacBook Retina), 3 (iPhone Pro).
Why do images look blurry on Retina displays? ▼
A 200×200 pixel image displayed at 200×200 CSS on a 2× DPR screen is stretched to 400×400 physical pixels, causing blur. The solution: use a 400×400 source image to match the physical pixel count.
How does pixel ratio affect website performance? ▼
Higher DPR images are larger files (4× file size at 2× DPR). Use responsive images (srcset attribute) to serve appropriately sized images based on DPR, balancing quality and page load speed.
What is the pixel ratio for 4K monitors? ▼
A 4K (3840×2160) monitor at native resolution has DPR 1.0. With Windows scaling at 150%, effective DPR ≈ 1.5. At 200% scaling (common on 27" 4K), DPR = 2.0, rendering content at 1920×1080 CSS pixels.