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.
Formules et Équations utilisées
Ce calculateur s'appuie sur 5 équations fondamentales :
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.
Comment utiliser ce calculateur
Pour utiliser ce Calculateur de Ratio, suivez ces 3 étapes :
Saisir les Valeurs
Saisissez les valeurs de ratio connues dans les champs. Laissez un champ vide — c'est la valeur manquante que le calculateur va chercher à résoudre.
Choisir le Mode
Sélectionnez le mode de ratio — Résoudre, Simplifier ou Mettre à l'échelle. Chaque mode applique des formules différentes à vos valeurs.
Obtenir les Résultats
Cliquez sur Calculer. L'écran de résultats affiche la réponse avec une barre de ratio interactive, un diagramme circulaire et le détail des calculs.
Exemples Pratiques et Solutions Étape par Étape
Voici 3 exemples de calculs résolus avec les étapes détaillées grâce à ce calculateur :
Saisie 1 iPhone 14 Pro: 393×852 CSS at 3× DPR
Saisie 2 Image for 2× and 3× displays
Saisie 3 Calculate DPR from screen specs
Foire Aux 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.