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Video Crop Calculator

Video & AudioEditing and Effects
Crop size (width × height) —
Top-left offset (centred)
—
Pixels removed
—
Share of frame kept
—
FFmpeg crop filter
—

To crop a video to a new aspect ratio, keep the dimension that already fits and cut the other: crop width = height × ratio, or crop height = width ÷ ratio. A 1920×1080 clip cropped to 4:3 becomes 1440×1080, offset 240 pixels from the left, which keeps 75% of the frame.

About this tool

Editors reframing landscape footage for Reels, Shorts, square feeds or a scope look need the exact crop box before they touch a timeline or an FFmpeg command. Enter the source resolution and pick a target ratio, or type your own, and the calculator returns the largest crop that fits, its centred top-left offset, how many pixels are removed on each axis and the share of the original frame that survives. Sizes are rounded to even numbers because most H.264 and HEVC encoders using 4:2:0 chroma reject odd widths and heights. The result also comes as a crop=w:h:x:y string you can paste into FFmpeg. One limit: the crop is always centred; if your subject sits off-centre, keep the size and shift the x or y offset by hand.

How to use it

  1. Enter the source resolution

    Type the width and height of the original clip in pixels, for example 3840 and 2160 for UHD.

  2. Choose the target ratio

    Pick a preset such as 9:16 or 4:5, or Custom ratio to enter any width and height pair like 3:2.

  3. Read the crop box

    Use the crop size, the centred offset and the FFmpeg string; the working shows which axis was trimmed.

Examples

1920×1080 to 4:3

Source width
1920
Source height
1080
Target aspect ratio
4:3 classic TV

Result Crop size (width × height): 1440 × 1080
Top-left offset (centred): x 240, y 0
Pixels removed: 480 px wide, 0 px tall
Share of frame kept: 75%
FFmpeg crop filter: crop=1440:1080:240:0

  1. Source 1920×1080 (1.7778) is wider than 1.3333, so the height is kept and the sides are cropped.
  2. Crop width = 1080 × 4 ÷ 3 = 1440 → 1440 (even)
  3. Offsets: x = (1920 − 1440) ÷ 2 = 240, y = (1080 − 1080) ÷ 2 = 0
  4. FFmpeg: crop=1440:1080:240:0

Pillarboxing a widescreen clip for a 4:3 delivery keeps the full height and trims 240 pixels from each side.

Landscape 1080p to a 9:16 Short

Source width
1920
Source height
1080
Target aspect ratio
9:16 vertical (Reels)

Result Crop size (width × height): 608 × 1080
Top-left offset (centred): x 656, y 0
Pixels removed: 1312 px wide, 0 px tall
Share of frame kept: 31.7%
FFmpeg crop filter: crop=608:1080:656:0

  1. Source 1920×1080 (1.7778) is wider than 0.5625, so the height is kept and the sides are cropped.
  2. Crop width = 1080 × 9 ÷ 16 = 607.5 → 608 (even)
  3. Offsets: x = (1920 − 608) ÷ 2 = 656, y = (1080 − 1080) ÷ 2 = 0
  4. FFmpeg: crop=608:1080:656:0

1080 × 9 ÷ 16 is 607.5, so the width rounds to the even 608 and under a third of the frame survives.

UHD to a 2.39:1 scope look

Source width
3840
Source height
2160
Target aspect ratio
2.39:1 cinemascope

Result Crop size (width × height): 3840 × 1606
Top-left offset (centred): x 0, y 277
Pixels removed: 0 px wide, 554 px tall
Share of frame kept: 74.4%
FFmpeg crop filter: crop=3840:1606:0:277

  1. Source 3840×2160 (1.7778) is not wider than 2.39, so the width is kept and top and bottom are cropped.
  2. Crop height = 3840 × 1 ÷ 2.39 = 1606.69 → 1606 (even)
  3. Offsets: x = (3840 − 3840) ÷ 2 = 0, y = (2160 − 1606) ÷ 2 = 277
  4. FFmpeg: crop=3840:1606:0:277

3840 ÷ 2.39 is 1606.7; the nearest even height that fits is 1606, leaving 277-pixel bars top and bottom.

How it is calculated

If W ÷ H ≥ a ÷ b: crop width = H × a ÷ b, crop height = H. Otherwise: crop width = W, crop height = W × b ÷ a. x = (W − crop width) ÷ 2, y = (H − crop height) ÷ 2

W, H
Source width and height in pixels
a : b
Target aspect ratio
x, y
Top-left corner of the centred crop

The frame's own ratio is compared with the target. A wider source keeps its full height and loses columns; a taller source keeps its full width and loses rows. The trimmed side is rounded to the nearest even pixel count, never above the source, because 4:2:0 chroma subsampling stores colour per 2×2 block. The offsets split the removed pixels equally between both edges, rounding down when the difference is odd.

When not to use it

  • Skip it when you want letterbox or pillarbox bars instead of cutting picture away.
  • It does not track a moving subject; reframing shots that pan needs keyframed crops.
  • Anamorphic footage with non-square pixels must be converted to its display size first.

Common mistakes

  • Entering the display resolution of a scaled preview rather than the file's true pixel size.
  • Using odd crop sizes, which many 4:2:0 encoders refuse or silently pad.
  • Cropping to 9:16 from 1080p and expecting 1080×1920 output without upscaling.

Frequently asked questions

Why is the crop width 608 and not 607.5 for 9:16 from 1080p?

1080 × 9 ÷ 16 equals 607.5, which is not a whole pixel. The calculator rounds to the nearest even number, 608, because H.264 and HEVC with 4:2:0 chroma need even dimensions. The ratio is then 0.5630 instead of exactly 0.5625, a difference no viewer will notice.

Which FFmpeg command applies these crop values?

Pass it to the video filter, for example ffmpeg -i in.mp4 -vf crop=608:1080:656:0 out.mp4. The four numbers are output width, output height, then the x and y position of the top-left corner. Add a scale filter afterwards if the platform expects a specific delivery size such as 1080×1920.

Can I move the crop off-centre?

Yes. The size stays the same; only the offset changes. x can be anything from 0 to the source width minus the crop width, and y from 0 to the source height minus the crop height. A 608-wide crop in a 1920 frame can start anywhere from x = 0 to x = 1312.

How much resolution do I lose cropping 4K to vertical?

From 3840×2160 to 9:16 the crop is 1216×2160, which keeps about 31.7% of the pixels. That is still enough to deliver a sharp 1080×1920 vertical video, which is why many creators shoot in 4K when they plan vertical cut-downs.

What does 2.39:1 mean compared with 21:9?

2.39:1 is the projection ratio for anamorphic cinema scope. Consumer 21:9 is a marketing name for roughly 2.33:1 to 2.37:1 displays. They look similar, but cropping UHD gives 1606 rows at 2.39:1 and 1646 rows at 21:9, so pick the one your delivery spec names.

Does cropping change the file's frame rate or duration?

No. A crop only removes pixels from each frame. Frame rate, duration and audio are untouched, though the bitrate needed for the same quality usually drops because there are fewer pixels to encode.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 24). Video Crop Calculator. Tools Directory. Retrieved October 26, 2026, from https://tools.milunir.com/video-audio/editing-and-effects/video-crop-calculator/

MLA

Tools Directory Editorial Team. “Video Crop Calculator.” Tools Directory, 24 Oct. 2026, https://tools.milunir.com/video-audio/editing-and-effects/video-crop-calculator/. Accessed 26 Oct. 2026.

Chicago

Tools Directory Editorial Team. “Video Crop Calculator.” Tools Directory. Last modified October 24, 2026. Accessed October 26, 2026. https://tools.milunir.com/video-audio/editing-and-effects/video-crop-calculator/.

Link<a href="https://tools.milunir.com/video-audio/editing-and-effects/video-crop-calculator/">Video Crop Calculator – Tools Directory</a>