Image Aspect Ratio Calculator

Enter width and height in pixels to calculate the aspect ratio instantly. Also scale images proportionally by entering a target width to find the matching height—essential for social media, video, web design, and print.

Calculator

Width (px)

Height (px)

Target Width (px)

Aspect Ratio

16:9

Decimal

1.778

Megapixels

2.07 MP

Scaled Size

1280×720

Common Aspect Ratios

Ratio	Common Use	Example Size
1:1	Instagram posts, profile pictures	1080×1080
4:3	Standard photos, iPad displays	1600×1200
16:9	YouTube, TV, widescreen monitors	1920×1080
9:16	Instagram/TikTok Stories, Reels	1080×1920
3:2	DSLR photos, 35mm film	1500×1000
21:9	Ultrawide monitors, cinema	2560×1080

How Aspect Ratio Is Calculated

The formula uses the Greatest Common Divisor (GCD) of width and height. Divide both dimensions by the GCD to get the simplest ratio. For 1920×1080: GCD = 120, so 1920÷120 : 1080÷120 = 16:9.

Worked Example

You have a 4000×3000 photo and need to resize it to 800px wide:

GCD of 4000 and 3000 = 1000 → Ratio = 4:3
Decimal ratio = 4000 ÷ 3000 = 1.333
New height = 800 ÷ 1.333 = 600px
Scaled size: 800×600

Frequently Asked Questions

What is aspect ratio?

Aspect ratio is the proportional relationship between width and height of an image or screen. It's expressed as two numbers separated by a colon (e.g., 16:9). It describes the shape, not the size—a 1920×1080 image and a 3840×2160 image are both 16:9.

How do I calculate aspect ratio?

Divide both the width and height by their greatest common divisor (GCD). For example, 1920×1080: GCD is 120, so 1920÷120 = 16 and 1080÷120 = 9, giving you 16:9.

What aspect ratio should I use for social media?

Instagram feed: 1:1 or 4:5. Instagram Stories/Reels: 9:16. YouTube: 16:9. Twitter/X: 16:9 or 2:1. Facebook: 1.91:1 for link previews, 1:1 for posts. TikTok: 9:16. LinkedIn: 1.91:1 or 1:1.

What happens if I use the wrong aspect ratio?

The platform will either crop your image (cutting off important content), add black bars (letterboxing/pillarboxing), or stretch/distort it. Always match the platform's recommended ratio for the best display.

How do I resize without changing aspect ratio?

Lock the aspect ratio in your image editor, then change only the width or height—the other dimension adjusts automatically. Our

calculator

helps you find the correct dimension when you know one side and the desired ratio.

Calculators & Reference Tools