Aspect Ratio Calculator - Image & Video Dimensions

What is an aspect ratio calculator?

An aspect ratio calculator helps you work with the proportional relationship between an image's or video's width and height. It determines the ratio from dimensions, calculates new sizes while maintaining proportions, and converts between standard formats.

Aspect ratios are essential for photographers, videographers, designers, and anyone working with digital media. Getting ratios right ensures your content displays correctly across different screens and platforms.

Understanding aspect ratio

An aspect ratio is expressed as two numbers separated by a colon, like 16:9 or 4:3. The first number represents width, the second represents height.

The ratio relationship

For a 16:9 aspect ratio:

• For every 16 units of width, there are 9 units of height
• A 1920×1080 image has 16:9 ratio (1920÷120 = 16, 1080÷120 = 9)
• A 3840×2160 image also has 16:9 ratio (scaled up 2×)

Calculating aspect ratio

To find the aspect ratio from dimensions:

1. Find the greatest common divisor (GCD) of width and height
2. Divide both dimensions by the GCD

Example: 1920 × 1080

• GCD of 1920 and 1080 = 120
• 1920 ÷ 120 = 16
• 1080 ÷ 120 = 9
• Aspect ratio = 16:9

Decimal form

Aspect ratios can also be expressed as decimals:

$$\text{Decimal Ratio} = \frac{\text{Width}}{\text{Height}}$$

Ratio	Decimal
16:9	1.778
4:3	1.333
1:1	1.000
21:9	2.333

Common aspect ratios

16:9 (widescreen)

The standard for modern displays:

Resolution	Name
1280×720	HD (720p)
1920×1080	Full HD (1080p)
2560×1440	QHD (1440p)
3840×2160	4K UHD
7680×4320	8K UHD

Used in: YouTube, TV broadcasts, computer monitors, streaming services

4:3 (classic)

The original television and early computer standard:

Resolution	Name
640×480	VGA
800×600	SVGA
1024×768	XGA
1600×1200	UXGA

Used in: iPad, classic TV shows, older photos, presentation slides

1:1 (square)

Equal width and height:

Resolution	Use
1080×1080	Instagram post
2048×2048	High-res square

Used in: Instagram posts, profile pictures, album covers, social media avatars

9:16 (vertical)

The inverse of 16:9 for mobile content:

Resolution	Use
1080×1920	Standard vertical
720×1280	Compressed vertical

Used in: TikTok, Instagram Reels, YouTube Shorts, Snapchat, Stories

21:9 (ultrawide)

Cinema and ultrawide displays:

Resolution	Name
2560×1080	UWFHD
3440×1440	UWQHD
5120×2160	5K Ultrawide

Used in: Ultrawide monitors, cinematic films, gaming

3:2 (photography)

Standard 35mm film ratio:

Resolution	Use
6000×4000	24MP camera
4500×3000	13.5MP

Used in: DSLR cameras, 35mm film, some laptops (Surface, MacBook)

4:5 (portrait)

Instagram's portrait format:

Resolution	Use
1080×1350	Instagram portrait
2160×2700	High-res portrait

Used in: Instagram portrait posts, vertical photographs

Resizing while maintaining ratio

When resizing images, maintaining aspect ratio prevents distortion.

Calculating new dimensions

If you know the original dimensions and want a specific width:

$$\text{New Height} = \frac{\text{New Width} \times \text{Original Height}}{\text{Original Width}}$$

Example: Resize 1920×1080 to 1280 width:

$$\text{New Height} = \frac{1280 \times 1080}{1920} = 720$$

Result: 1280×720 (maintains 16:9)

If you know the target height:

$$\text{New Width} = \frac{\text{New Height} \times \text{Original Width}}{\text{Original Height}}$$

Platform-specific requirements

Social media

Platform	Format	Dimensions
Instagram Post	1:1	1080×1080
Instagram Portrait	4:5	1080×1350
Instagram Story/Reel	9:16	1080×1920
YouTube Thumbnail	16:9	1280×720
YouTube Video	16:9	1920×1080
TikTok	9:16	1080×1920
Twitter Post	16:9	1200×675
Twitter Header	3:1	1500×500
Facebook Post	1.91:1	1200×630
LinkedIn Post	1.91:1	1200×627

Print media

Format	Ratio	Common sizes
Photo prints	3:2	4×6, 6×9, 8×12
Standard paper	~1.41:1	A4, Letter
Square	1:1	5×5, 8×8, 12×12
Panoramic	3:1	4×12, 6×18

Cropping and letterboxing

When source and target ratios don't match, you have two options:

Cropping (fill)

Removes parts of the image to fill the target ratio. You lose content but fill the entire frame.

Example: Fitting 4:3 content into 16:9

• Original: 1600×1200
• Crop height to: 1600×900
• Lost: 300 pixels (25%) from top/bottom

Letterboxing/Pillarboxing (fit)

Adds black bars to preserve all content.

• Letterboxing: Horizontal bars (top/bottom) when fitting wider content into taller frame
• Pillarboxing: Vertical bars (left/right) when fitting taller content into wider frame

Example: Fitting 4:3 content into 16:9

• Original displays at: 1440×1080 (centered)
• Black bars: 240 pixels each side

Pixels and resolution

Total pixels

$$\text{Total Pixels} = \text{Width} \times \text{Height}$$

Megapixels

$$\text{Megapixels} = \frac{\text{Width} \times \text{Height}}{1,000,000}$$

Resolution	Megapixels
1920×1080	2.07 MP
2560×1440	3.69 MP
3840×2160	8.29 MP
4000×6000	24 MP

DPI/PPI considerations

Pixels per inch determines print quality:

DPI	Quality	Use
72	Screen	Web, digital only
150	Draft	Proofs, drafts
300	Print	Professional printing
600+	High-res	Fine art, detailed work

To calculate print size:

$$\text{Print Size (inches)} = \frac{\text{Pixel Dimension}}{\text{DPI}}$$

Example: 3000×2000 at 300 DPI = 10×6.67 inch print

Video aspect ratios

Frame rates and resolution

Standard	Resolution	Ratio	Frame rates
720p HD	1280×720	16:9	30, 60 fps
1080p FHD	1920×1080	16:9	24, 30, 60 fps
1440p QHD	2560×1440	16:9	30, 60 fps
4K UHD	3840×2160	16:9	24, 30, 60 fps
4K DCI	4096×2160	1.9:1	24 fps

Cinema standards

Format	Ratio	Decimal
Academy	1.37:1	1.375
Flat	1.85:1	1.85
Scope	2.39:1	2.39
IMAX	1.43:1	1.43

Display technologies

Monitor aspect ratios

Type	Ratio	Example resolutions
Standard	16:9	1920×1080, 2560×1440
Ultrawide	21:9	2560×1080, 3440×1440
Super ultrawide	32:9	3840×1080, 5120×1440
Vertical	9:16	1080×1920

Mobile screens

Device	Ratio	Resolution
iPhone 15	19.5:9	2556×1179
Samsung Galaxy	19.5:9	3088×1440
iPad	4:3	2048×1536
iPad Pro	4:3	2732×2048

Working with aspect ratios

Responsive design

For web design, use CSS aspect-ratio property:

.video-container {
  aspect-ratio: 16 / 9;
  width: 100%;
}

Padding trick (legacy)

Before the aspect-ratio property:

.container {
  position: relative;
  padding-bottom: 56.25%; /* 9/16 = 0.5625 */
}

Image containers

When fitting images into containers:

• object-fit: cover - Fills container, crops excess
• object-fit: contain - Fits inside, may letterbox
• object-fit: fill - Stretches to fill (distorts)

Frequently asked questions

What aspect ratio is 1920×1080?

1920×1080 is a 16:9 aspect ratio. Dividing both by 120 (their GCD) gives 16:9.

How do I maintain aspect ratio when resizing?

Multiply or divide both width and height by the same factor, or use this formula: New Height = (New Width × Original Height) ÷ Original Width

What's the best aspect ratio for Instagram?

• Square posts: 1:1 (1080×1080)
• Portrait posts: 4:5 (1080×1350)
• Stories/Reels: 9:16 (1080×1920)

Why does my video have black bars?

Black bars appear when the video's aspect ratio doesn't match the display's ratio. The bars preserve the original proportions rather than stretching the content.

How do I convert 4:3 to 16:9?

You must either crop the top/bottom of the 4:3 content or add pillarboxing (black bars on the sides). There's no way to convert without losing content or adding bars.

What resolution is 4K?

4K UHD is 3840×2160 (16:9 ratio). Cinema 4K (DCI) is 4096×2160 (slightly wider at 1.9:1).