Display Basics

What is Aspect Ratio? Complete Guide to 16:9, 21:9, 4:3 and More

· 14 min read

Aspect ratio is one of the most fundamental concepts in displays, photography, and video production—yet it’s often misunderstood. Whether you’re buying a new TV, editing video, or wondering why black bars appear on your screen, understanding aspect ratios will help you make better decisions.

This guide explains what aspect ratio means, covers all common ratios, and shows you how to choose the right one for your needs. You can also use our aspect ratio calculator to convert between different ratios instantly.

What is Aspect Ratio?

Aspect ratio is the proportional relationship between a screen’s width and height, expressed as two numbers separated by a colon (e.g., 16:9).

Aspect Ratio = Width : Height

Example: 16:9
┌────────────────────────────┐
│                            │
│         16 units           │
│      ←───────────→         │  9 units
│                            │  ↕
│                            │
└────────────────────────────┘

Key points:

  • Aspect ratio describes shape, not size
  • A 16:9 screen could be 32” or 65”—both have the same shape
  • The numbers are typically simplified (1920×1080 simplifies to 16:9)

Mathematical Definition: Aspect ratio is the ratio of width to height. For a 1920×1080 display: 1920÷1080 = 1.78, which equals 16÷9. [Source: SMPTE ST 2067-21]

Common Aspect Ratios Explained

16:9 — The Modern Standard

Also known as: 1.78:1, Widescreen, HDTV

Where it’s used:

  • HDTVs and 4K TVs
  • Computer monitors
  • YouTube videos
  • Most streaming content
  • Video games
ResolutionAspect RatioCommon Name
1280×72016:9HD / 720p
1920×108016:9Full HD / 1080p
2560×144016:9QHD / 1440p
3840×216016:94K UHD
7680×432016:98K UHD

Why 16:9 became standard:

In 2009, the Society of Motion Picture and Television Engineers (SMPTE) and international standards bodies adopted 16:9 as the universal HD standard because it’s a mathematical compromise between the old 4:3 TV format and wider cinema formats.

16:9 is a compromise:
4:3 (1.33)  ████████████░░░░░░░░░░░░░░░░░░░░
16:9 (1.78) ████████████████████░░░░░░░░░░░░
2.39:1      ████████████████████████████████
            ↑ Narrower              Wider ↑

4:3 — The Classic Format

Also known as: 1.33:1, Standard Definition, Academy Ratio

Where it’s used:

  • Old CRT televisions
  • Classic films (pre-1950s)
  • iPad displays
  • Some professional monitors
  • Retro gaming
ResolutionAspect RatioEra
640×4804:3VGA
800×6004:3SVGA
1024×7684:3XGA
1600×12004:3UXGA
2048×15364:3iPad Retina

Historical context:

The 4:3 ratio dates back to Thomas Edison’s film experiments in the 1890s. It became the standard for television when broadcasts began in the 1940s-50s, matching the existing film format.

Fun Fact: Apple chose 4:3 for iPads because it’s optimal for reading documents and web pages in both orientations—closer to paper proportions than 16:9.

21:9 — Ultrawide / Cinematic

Also known as: 2.33:1, 2.35:1, 2.39:1, Ultrawide, CinemaScope

Where it’s used:

  • Ultrawide monitors
  • Cinematic films
  • Some flagship smartphones
  • Immersive gaming
ResolutionAspect RatioCommon Name
2560×108021:9UWFHD
3440×144021:9UWQHD
3840×160021:9UWQHD+
5120×216021:95K Ultrawide

Cinema aspect ratios (technically different but grouped as “21:9”):

RatioDecimalNameUsed In
2.35:12.35CinemaScopeClassic widescreen films
2.39:12.39PanavisionModern blockbusters
2.40:12.40ScopeIndustry standard today

Industry Standard: According to the American Society of Cinematographers, approximately 70% of theatrical releases use a 2.39:1 aspect ratio, while 30% use 1.85:1.

32:9 — Super Ultrawide

Also known as: 3.56:1, DFHD (Dual Full HD)

Where it’s used:

  • Super ultrawide monitors
  • Equivalent to two 16:9 monitors side by side
  • Professional workstations
  • Immersive simulation gaming
ResolutionAspect RatioEquivalent To
3840×108032:92× 1920×1080
5120×144032:92× 2560×1440

Other Notable Aspect Ratios

RatioDecimalNamePrimary Use
1:11.00SquareInstagram posts, album art
3:21.50Classic PhotoDSLR photos, Surface devices
5:41.25SXGAOlder LCD monitors
1.85:11.85Flat WidescreenMany theatrical films
9:160.56Vertical VideoTikTok, Instagram Stories
19.5:92.17Tall PhoneModern smartphones
20:92.22Tall PhoneSamsung Galaxy series

Aspect Ratio in Different Contexts

Television and Streaming

When choosing a TV, aspect ratio affects how content appears on screen. Learn more about how to choose the right TV size for your room or use our TV screen size calculator to find the perfect fit.

Content TypeNative RatioOn 16:9 TV
Modern TV shows16:9Full screen
Classic TV (pre-2000)4:3Pillarboxed (black bars on sides)
Theatrical films2.39:1Letterboxed (black bars top/bottom)
IMAX scenes1.43:1 or 1.90:1Varies

Understanding black bars:

Letterboxing (wide content on 16:9):
┌────────────────────────────┐
│▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ ← Black bar
│                            │
│     2.39:1 Movie Content   │
│                            │
│▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓│ ← Black bar
└────────────────────────────┘

Pillarboxing (narrow content on 16:9):
┌────────────────────────────┐
│▓▓▓│                  │▓▓▓▓│
│▓▓▓│   4:3 Content    │▓▓▓▓│
│▓▓▓│                  │▓▓▓▓│
│▓▓▓│                  │▓▓▓▓│
└────────────────────────────┘
  ↑                      ↑
Black bars            Black bars

Streaming Note: Netflix, Disney+, and other services preserve original aspect ratios. Films shot in 2.39:1 will have letterboxing on 16:9 TVs—this is intentional and preserves the director’s vision.

Smartphones

Modern smartphones have moved away from 16:9 to taller ratios. Compare different phone screen sizes with our phone screen size calculator.

PhoneAspect RatioWhy
iPhone 15 Pro19.5:9More content while scrolling
Samsung Galaxy S2419.5:9One-handed usability
Google Pixel 820:9Optimized for apps
Sony Xperia 1 VI21:9Cinematic video playback

Why phones went taller:

  • More content visible when scrolling
  • Better one-handed reach (narrower)
  • Cinematic video without letterboxing
  • Split-screen multitasking

Photography

RatioUse CaseCameras
3:2Standard photosDSLRs, mirrorless
4:3Compact camerasMicro Four Thirds, phones
1:1Square formatMedium format, Instagram
16:9Video stillsAction cameras
65:24PanoramicXPan, panorama mode

Print Consideration: Standard photo print sizes (4×6, 5×7, 8×10) don’t match common camera ratios, which is why cropping is often needed. A 3:2 photo fits 4×6 prints perfectly but requires cropping for 8×10.

Video Production

PlatformRecommended RatioResolution
YouTube16:91920×1080 or 3840×2160
TikTok9:161080×1920
Instagram Feed1:1 or 4:51080×1080 or 1080×1350
Instagram Reels9:161080×1920
Twitter/X16:9 or 1:11280×720 or 720×720
Cinema2.39:14096×1716 (4K DCI)

How to Calculate Aspect Ratio

Method 1: Divide Width by Height

Aspect Ratio = Width ÷ Height

Example: 1920×1080
1920 ÷ 1080 = 1.778 (which is 16÷9)

Method 2: Find Greatest Common Divisor (GCD)

1920×1080
GCD(1920, 1080) = 120

1920 ÷ 120 = 16
1080 ÷ 120 = 9

Aspect Ratio = 16:9

Common Resolution to Aspect Ratio

ResolutionCalculationAspect Ratio
1920×10801920/1080 = 1.7816:9
2560×14402560/1440 = 1.7816:9
3440×14403440/1440 = 2.3921:9 (≈43:18)
2048×15362048/1536 = 1.334:3
5120×14405120/1440 = 3.5632:9

Aspect Ratio Decimal Reference

RatioDecimalVisual Width
1:11.00████████
5:41.25██████████
4:31.33███████████
3:21.50████████████
16:101.60█████████████
16:91.78██████████████
1.85:11.85███████████████
2:12.00████████████████
21:92.33██████████████████
2.39:12.39███████████████████
32:93.56████████████████████████████

Aspect Ratio and Screen Size

Same Diagonal, Different Area

Two screens with the same diagonal measurement but different aspect ratios have different actual viewing areas:

DiagonalAspect RatioWidthHeightArea
55”16:947.9”27.0”1,293 sq in
55”21:950.8”21.8”1,107 sq in
55”4:344.0”33.0”1,452 sq in

Important: A 55” ultrawide (21:9) has 14% less viewing area than a 55” standard (16:9) TV, despite the same diagonal measurement.

Calculating Dimensions from Diagonal

Formula:

Width = Diagonal × cos(arctan(Height Ratio / Width Ratio))
Height = Diagonal × sin(arctan(Height Ratio / Width Ratio))

Simplified for common ratios:

RatioWidth FactorHeight Factor
16:90.8720.490
21:90.9240.396
4:30.8000.600
32:90.9620.271

Example: 65” TV at 16:9

  • Width = 65 × 0.872 = 56.7”
  • Height = 65 × 0.490 = 31.9”

Use our aspect ratio calculator for instant calculations.

Choosing the Right Aspect Ratio

For TVs

Use CaseBest RatioWhy
General viewing16:9Universal compatibility
Movie enthusiast16:9 (accept letterboxing)Most content is 16:9 or wider
Retro gaming16:9 with 4:3 modeCan display both

Should you buy an ultrawide TV?

No consumer ultrawide TVs exist because:

  • Most content is 16:9
  • Broadcast standards are 16:9
  • Would require letterboxing for most content

For Monitors

For detailed guidance on choosing the right monitor, check out our monitor size guide or use the monitor screen size calculator.

Use CaseBest RatioRecommended
General productivity16:927” 1440p
Heavy multitasking21:934” 3440×1440
Dual-monitor replacement32:949” 5120×1440
Photo editing16:9 or 3:2Color-accurate panel
Video editing21:9Timeline benefits (see our video editing monitor guide)
Competitive gaming16:9Tournament standard
Immersive gaming21:9Wider FOV

For Content Creation

Content TypeShoot InDeliver In
YouTube16:916:9
TikTok/Reels9:169:16
Instagram Feed1:1 or 4:51:1 or 4:5
Theatrical film2.39:12.39:1
Corporate video16:916:9
Vertical ads9:169:16

Aspect Ratio Problems and Solutions

Problem: Black Bars on Screen

Cause: Content aspect ratio doesn’t match display aspect ratio.

Solutions:

SituationSolutionTrade-off
Movie on 16:9 TVAccept letterboxingNone—this is correct
4:3 content on 16:9Accept pillarboxingNone—preserves original
Stretch to fillNot recommendedDistorts image
Zoom to fillPossibleCrops content

Best Practice: Never stretch content to fill the screen. Letterboxing and pillarboxing preserve the original composition. Stretching distorts faces and objects unnaturally.

Problem: Cropped Content

Cause: Displaying wider content on narrower screen (or vice versa) with zoom enabled.

Example: 2.39:1 movie zoomed to fill 16:9 TV

  • 25% of horizontal content is cropped
  • Director’s composition is ruined

Problem: Game Doesn’t Support Ultrawide

Solutions:

  1. Check PCGamingWiki — Community fixes often exist
  2. Use third-party tools — Flawless Widescreen, hex edits
  3. Accept pillarboxing — Play at 16:9 with black bars
  4. GPU scaling — Some GPUs can stretch (not recommended)

Historical Evolution of Aspect Ratios

Timeline

EraDominant RatioTechnology
1890s-1950s4:3 (1.33:1)Film, early TV
1950s-1970sVarious widescreenCinemaScope, Panavision
1980s-2000s4:3 (TV), 1.85/2.39 (film)CRT televisions
2000s-2010s16:9HDTV transition
2010s-present16:9 (TV), 21:9 (monitors)4K, ultrawide adoption
2020s16:9, 21:9, tall phonesDiverse ecosystem

Why Widescreen Won

In the 1950s, television threatened cinema. Hollywood responded with widescreen formats (CinemaScope, Panavision) to offer an experience TV couldn’t match. These wider ratios:

  • Created more immersive experiences
  • Better matched human peripheral vision
  • Differentiated theatrical releases from TV

Historical Note: The Academy of Motion Picture Arts and Sciences standardized the “Academy Ratio” (1.375:1, nearly 4:3) in 1932, which remained dominant until widescreen formats emerged in the 1950s.

Quick Reference Chart

Aspect Ratio Visual Comparison

1:1    ████████
4:3    ██████████
3:2    ████████████
16:10  █████████████
16:9   ██████████████
1.85:1 ███████████████
2:1    ████████████████
21:9   ██████████████████
2.39:1 ███████████████████
32:9   ████████████████████████████

Common Resolutions by Aspect Ratio

Aspect RatioResolutions
4:3640×480, 800×600, 1024×768, 1600×1200, 2048×1536
16:101280×800, 1440×900, 1680×1050, 1920×1200, 2560×1600
16:91280×720, 1920×1080, 2560×1440, 3840×2160, 7680×4320
21:92560×1080, 3440×1440, 3840×1600, 5120×2160
32:93840×1080, 5120×1440

Conclusion

Understanding aspect ratio helps you:

  • Choose the right display for your content consumption habits
  • Create content optimized for your target platform
  • Understand why black bars appear (and why that’s often correct)
  • Compare screen sizes accurately across different ratios

Key takeaways:

RatioBest For
16:9Universal standard—TVs, monitors, YouTube
4:3Tablets, classic content, documents
21:9Ultrawide monitors, cinematic content
9:16Vertical video (TikTok, Stories)
1:1Social media posts, album art

Use our aspect ratio calculator to convert between ratios and calculate exact dimensions for any screen size.

Frequently Asked Questions

What is the most common aspect ratio for TVs and monitors?

16:9 is the most common aspect ratio for modern TVs, computer monitors, and video content. It became the universal HD standard in 2009 and is used for all HD, 4K, and 8K resolutions. If you’re buying a TV or monitor for general use, 16:9 is the safest choice as virtually all content is optimized for this ratio.

Why do movies have black bars on my TV?

Black bars (called letterboxing) appear because most theatrical films are shot in wider aspect ratios like 2.39:1, while your TV is 16:9 (1.78:1). The black bars preserve the director’s original composition—stretching or cropping the image would distort faces and cut off important visual information. This is the correct way to display widescreen content.

Is 21:9 ultrawide better than 16:9?

It depends on your use case:

  • Choose 21:9 if you prioritize immersive gaming, video editing timelines, or multitasking with multiple windows side by side
  • Choose 16:9 if you watch a lot of standard video content, play competitive esports games, or need a dedicated 4K preview for video work

Most 21:9 ultrawides cannot display 4K content at 100% scale, which matters for professional video editing.

How do I calculate the aspect ratio of my screen?

Divide your screen’s width by its height. For example:

  • 1920 ÷ 1080 = 1.78 (which is 16:9)
  • 3440 ÷ 1440 = 2.39 (which is 21:9)

You can also use our aspect ratio calculator for instant conversions.

What aspect ratio should I use for social media videos?

PlatformRecommended Ratio
YouTube16:9
TikTok / Instagram Reels9:16 (vertical)
Instagram Feed1:1 or 4:5
Twitter/X16:9 or 1:1

References