Aspect Ratio Calculator: Resize, Letterbox and Crop
An aspect ratio is the width divided by the height, reduced to its smallest whole numbers: 1920 x 1080 is 16:9. To resize without distortion, multiply the new width by the height over the width. To place a clip in a frame with a different ratio you either scale it to fit, which adds bars, or scale it to fill, which crops the edges. The calculator shows all three.
Aspect ratio calculator
Enter your clip's size. Results update as you type and the numbers are saved in the page address. Nothing leaves your browser. All sizes are in pixels.
How the aspect ratio calculator works
The ratio is the width over the height. Dividing both by their greatest common divisor gives the smallest whole-number form. Resizing keeps that ratio, so one side fixes the other. Placing a clip in a frame with a different ratio is a choice between two scales: the smaller one keeps the whole picture and leaves bars, the larger one covers the frame and crops the overflow.
ratio = (width ÷ g) : (height ÷ g), g = greatest common divisor new height = new width × height ÷ width fit scale = smaller of (frame width ÷ width, frame height ÷ height) fill scale = larger of the same two bar (each side) = (frame side − scaled side) ÷ 2 crop (each side) = (scaled side − frame side) ÷ 2 at the fill scale
- g
- greatest common divisor of width and height
- frame
- the output frame the clip is placed in
Worked example
Given: a 1920 x 1080 clip; placed in a 1080 x 1920 vertical frame; resized to 1280 wide.
- Ratio:
gcd(1920, 1080) = 120, so 1920 ÷ 120 : 1080 ÷ 120 = 16:9 - Height at 1280 wide:
1280 × 1080 ÷ 1920 = 720 - Fit scale:
min(1080 ÷ 1920, 1920 ÷ 1080) = min(0.5625, 1.7778) = 0.5625 - Fitted size:
1920 × 0.5625 = 1080 wide, 1080 × 0.5625 = 607.5 high - Bars (top and bottom):
(1920 − 607.5) ÷ 2 = 656.25 px each - Fill scale:
1920 ÷ 1080 = 1.7778, giving 3413.3 × 1920, so 1166.7 px is cropped from each side
Answer: 16:9; 720 high at 1280 wide; fitted in the vertical frame it is 1080 × 607.5 with about 656 px bars, or filled it loses about 68% of its width to cropping.
Frame sizes in Apple's ProRes tables
| Frame size | Name used | Ratio | Decimal |
|---|---|---|---|
| 1280 x 720 | 720p HD | 16:9 | 1.778 |
| 1920 x 1080 | Full HD (1080p) | 16:9 | 1.778 |
| 2048 x 1080 | 2K (DCI container) | 256:135 | 1.896 |
| 3840 x 2160 | QFHD / UHD 4K | 16:9 | 1.778 |
| 4096 x 2160 | 4K (DCI container) | 256:135 | 1.896 |
| 5120 x 2700 | 5K | 256:135 | 1.896 |
Source 1. Ratios and decimals are our arithmetic from the published sizes.
Assumptions and limits
- Pixel aspect ratio is assumed square. Anamorphic or non-square-pixel footage has a display ratio different from its stored size; enter the display size.
- Sizes are not rounded for codec rules. Many encoders want even numbers or multiples of a block size; check your encoder's documentation (not confirmed here).
- Fitted sizes can have fractions of a pixel; round to the pixel your editor uses.
- Rotation metadata (a phone clip stored sideways) is not read; enter the size you see on screen.
- Frame sizes in the table come from Apple's ProRes tables and are not a list of every standard size.
Frequently asked questions
What aspect ratio is 1920 x 1080?
16:9. Divide both numbers by their greatest common divisor, 120, to get 16 and 9. 3840 x 2160 and 1280 x 720 reduce to 16:9 as well, which is why they scale into each other without bars. YouTube states that 16:9 is the standard aspect ratio for its player on a computer.
Why is 4096 x 2160 not 16:9?
It reduces to 256:135, a decimal of about 1.896 against 1.778 for 16:9. Apple's ProRes white paper lists it as the 4K size next to 3840 x 2160 (QFHD). Putting a 4096 x 2160 clip in a 3840 x 2160 frame leaves thin bars at top and bottom; the calculator shows how thick.
How do I resize a video without stretching it?
Change one side and compute the other from the ratio. New height = new width × original height ÷ original width. For 1920 x 1080 resized to 1280 wide that is 1280 × 1080 ÷ 1920 = 720. If the result is not a whole number, most editors need you to round to a whole pixel, which slightly changes the ratio.
What is the difference between letterbox and pillarbox?
Letterbox bars sit above and below the picture, which happens when the clip is wider than the frame. Pillarbox bars sit left and right, which happens when the clip is taller or narrower than the frame, such as a 4:3 clip in a 16:9 frame. Scale to fit keeps the whole picture and adds bars.
How do I turn a 16:9 video into a vertical 9:16 one?
There are two ways. Scale to fit puts the whole 16:9 picture across the frame and leaves bars above and below; for 1920 x 1080 into 1080 x 1920 the picture becomes 1080 x 607.5 with bars of about 656 pixels each. Scale to fill enlarges the clip until it covers the frame and crops the sides, losing about 68% of the width. Enter those sizes above to see the figures for your clip.
What aspect ratio does YouTube need?
YouTube says the standard ratio on a computer is 16:9 and that when you upload other ratios such as vertical or square, the player adapts itself to the size of the video. The page does not give a pixel size for vertical video, so we do not state one.
Does the calculator tell me which codec or converter to use?
No. It only does the geometry. For codec and file size questions see the file size calculator.
Sources
- Apple, Apple ProRes White Paper (April 2017): frame sizes in the target data rate tables (apple.com) Accessed 2026-11-13.
- YouTube Help, YouTube recommended upload encoding settings: video resolution and aspect ratio (support.google.com) Accessed 2026-11-13.