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Aspect ratio calculator (16:9, 4:3, 21:9)

Find the aspect ratio of any resolution, such as 1920 × 1080 = 16:9, resize it to a new width or height, or fit it in a screen with letterbox bars.

업데이트 검증한 예제: 9

px
px
시도하기
Simplified ratio
16:9
Simplified ratio: 16:9
Width ÷ height
1.7778
Closest common ratio
16:9

1,920 × 1,080 simplifies to 16:9: the width is 1.7778 times the height.

Shape

16:91,920 px1,080 px
계산 방법 S

  1. Divide both sides by their greatest common divisor

    gcd⁡(1920,1080)=120,1920120:1080120=16:9\gcd(1920, 1080) = 120,\quad \frac{1920}{120} : \frac{1080}{120} = 16 : 9

  2. As a single number

    1,9201,080=1.7778\frac{1{,}920}{1{,}080} = 1.7778

Aspect ratio calculator (16:9, 4:3, 21:9) 소개

The aspect ratio is the width divided by the height, written in lowest terms by dividing both sides by their greatest common divisor: 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so 1920 × 1080 is 16:9. Resizing keeps that quotient fixed, so the new height is the new width × H ÷ W. Fitting a picture inside another frame uses the largest scale that fits both ways, s = min(frame width ÷ W, frame height ÷ H), and the leftover space becomes bars.

Scaling 1920 × 1080 to 1280 wide gives 1280 × 720. Showing that 16:9 picture on a 1024 × 768 screen gives a 1024 × 576 picture with 96 px letterbox bars above and below, so the picture uses 75% of the screen.

Sizes stay exact fractions until the end. Scaled sizes are then rounded to whole pixels, which can shift the ratio slightly.

계산 예제

Full HD

I want to
Find the ratio
너비
1920 px
높이
1080 px
Simplified ratio
16:9
Width ÷ height
1.7778
Closest common ratio
16:9

검증 출처: Python 3.8: fractions.Fraction(1920, 1080) = 16/9

Ultrawide 2560 × 1080

I want to
Find the ratio
너비
2560 px
높이
1080 px
Simplified ratio
64:27
Width ÷ height
2.3704

검증 출처: Python 3.8: fractions.Fraction(2560, 1080) = 64/27 = 2.37037…

1366 × 768 laptop is not exactly 16:9 (edge)

I want to
Find the ratio
너비
1366 px
높이
768 px
Simplified ratio
683:384
Width ÷ height
1.7786
Closest common ratio
16:9 (0.05% wider)

검증 출처: Python 3.8: Fraction(1366, 768) = 683/384; (683/384) / (16/9) − 1 = 0.0488%

Decimal cinema ratio

I want to
Find the ratio
너비
2.39 px
높이
1 px
Simplified ratio
239:100

검증 출처: Python 3.8: Fraction('2.39') / 1 = 239/100

자주 묻는 질문

What is the aspect ratio of 1920 × 1080?

1920 × 1080 is 16:9: both sides divide by their greatest common divisor, 120, to give 16 and 9, and the width is 1.7778 times the height. ITU-R BT.709 defines 1920 × 1080 as the HDTV picture format, and the same 16:9 shape covers 1280 × 720, 2560 × 1440 and 3840 × 2160 (4K UHD).

Is a 21:9 ultrawide monitor really 21:9?

No. Ultrawide monitors sold as 21:9 are 2560 × 1080 (64:27, 2.370), 3440 × 1440 (43:18, 2.389) or 3840 × 1600 (12:5, 2.4), while 21:9 itself is 2.333. The label is rounded marketing, and the gap shows up in practice: true 21:9 video on a 3440 × 1440 panel fills 3360 × 1440 and leaves a 40 px pillarbox bar on each side.

How do I calculate the new height when resizing an image?

Multiply the new width by the original height over the original width: new height = new width × H ÷ W. Scaling 1920 × 1080 to 1280 wide gives 1280 × 1080 ÷ 1920 = 720. The other way round, new width = new height × W ÷ H, so a 4:3 picture 1080 tall is 1440 wide. Round to whole pixels at the end, and to even numbers for most video encoders.

What is the difference between letterbox and pillarbox?

Letterboxing adds bars above and below when the picture is wider than the screen, such as 16:9 video on a 1024 × 768 display, which gets 96 px bars. Pillarboxing adds bars on the left and right when the picture is narrower, such as 4:3 content on a 1920 × 1080 screen, which leaves 240 px on each side. Zooming to fill removes the bars but crops the picture, by 25% in that 4:3 case.

What aspect ratios do cinema films use?

Digital cinema uses two DCI container shapes: flat at 1.85:1 (1998 × 1080 in the 2K container) and scope at 2.39:1 (2048 × 858). On a 1920 × 1080 TV, a 2.39:1 film shows letterbox bars of about 138 px above and below, and a 1.85:1 film bars of about 21 px, because both are wider than the TV's 16:9 (1.78:1).

“Aspect ratio calculator (16:9, 4:3, 21:9)”의 정확도는 어느 정도인가요?

정확도는 입력값과 계산 방법의 가정에 따라 달라집니다. 십진 연산은 유효숫자 50자리를 사용하지만, 추정값·수치해석 방법·원본 데이터의 정밀도는 더 낮을 수 있습니다. 표시값을 반올림해도 이러한 한계는 사라지지 않습니다. 독립적인 출처의 풀이와 대조한 계산 예시: 9. 예를 들어 “Full HD”은 Python 3.8: fractions.Fraction(1920, 1080) = 16/9와 대조해 확인합니다.

이 계산 방법의 출처는 무엇인가요?

ITU-R BT.709-6 — HDTV picture format 1920 × 1080 at 16:9; DCI Digital Cinema System Specification — flat 1998 × 1080 (1.85:1) and scope 2048 × 858 (2.39:1) containers.

이 계산기 소개

W:H=Wgcd⁡(W,H):Hgcd⁡(W,H)s=min⁡ ⁣(WfW,HfH)\begin{aligned} W{:}H &= \frac{W}{\gcd(W,H)} : \frac{H}{\gcd(W,H)} \\[4pt] s &= \min\!\left(\frac{W_f}{W}, \frac{H_f}{H}\right)\end{aligned}

출처

  1. ITU-R BT.709-6 — HDTV picture format 1920 × 1080 at 16:9
  2. DCI Digital Cinema System Specification — flat 1998 × 1080 (1.85:1) and scope 2048 × 858 (2.39:1) containers

출처와 대조하여 검증

이 계산기에는 독립적인 출처에서 답을 얻은 계산 예제가 9개 있습니다. 테스트 모음에서 실행되며 여기에서도 실행할 수 있습니다.

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