Instagram video size refers to one of three pixel rectangles — 1080 × 1080 for a 1:1 square Feed post, 1080 × 1350 for a 4:5 portrait Feed post, or 1080 × 1920 for a 9:16 Story or Reel — and the Video Cropper reaches each one by recording an exact X, Y, width, and height region of the source frame. Cropping removes the outer frame of every source frame; it does not resize, stretch, pad, or letterbox the picture. That distinction matters because Instagram's pixel sizes differ by surface, and the rectangle you enter must fit inside the source dimensions in whole, nonnegative pixels. The tool plays the source locally in your browser, draws only the selected region into a Canvas at 30 fps, records that Canvas stream as a WebM file, and patches in a finite Matroska duration so the output plays correctly. Your source never uploads, and processing time matches playback time — a one-minute clip takes about one minute while the tab stays open. The rest of this guide walks through the pixel math for each format, the exact steps to apply it, and the limits that can stop a crop before it starts.
Instagram's Three Main Video Aspect Ratios
Instagram does not publish a single "Instagram size" for video. Each upload surface accepts a different rectangle of pixels, and the rectangle that works on one surface will be wrong for another. Three ratios cover virtually every post: a 1:1 square for the Feed grid, a 4:5 portrait for taller Feed posts, and a 9:16 vertical for full-screen Stories and Reels.
| Surface | Aspect ratio | Common pixel size | Where it shows |
|---|---|---|---|
| Feed (square) | 1:1 | 1080 × 1080 | Timeline grid; equal width and height |
| Feed (portrait) | 4:5 | 1080 × 1350 | Maximizes vertical real estate in the mobile feed |
| Story | 9:16 | 1080 × 1920 | Full-screen vertical, expires after 24 hours |
| Reels | 9:16 | 1080 × 1920 | Same rectangle as Story; shorter duration caps apply |
The Video Cropper has no built-in knowledge of which surface you are targeting, so the choice is yours. Pick the row that matches the destination, then translate the pixel size into X, Y, width, and height against your actual source dimensions in the next sections.
What "Crop" Actually Changes in the Frame
Cropping selects a fixed rectangular region of every frame and discards everything outside it. It does not scale the picture up, scale it down, add black bars, or letterbox. The output pixel count is exactly width × height from your inputs — no more, no less — and the visible content shifts according to where X and Y land. With a 1920 × 1080 (16:9) source you can reach 1:1 and 4:5 cleanly because the source has enough horizontal pixels to spare. You cannot reach 9:16 from that same source in a single crop, because a true 9:16 rectangle needs more vertical pixels than 1080, and the source height is already only 1080. For that conversion you would resize the source first or letterbox it with a complementary tool, then crop if needed.
How Video Cropper Produces the Cropped Frame
When you choose a browser-decodable video, the Video Cropper reads its decoded dimensions in the current tab. After you enter X, Y, width, and height, the tool validates that every value is an untrimmed nonnegative whole pixel count, that width and height are each at least two, and that X + width and Y + height remain inside the decoded source. It also checks that the output area does not exceed 3840 × 2160 pixels. Once validated, the source plays locally at native rate.
Each frame is drawn into an equal-size opaque Canvas, capturing only the rectangle you requested; the rest never enters the Canvas. The Canvas stream is then handed to MediaRecorder, which records WebM using the first supported codec the browser reports (VP9, then VP8, then generic WebM). Requested bitrate is bounded between 180 kbps and 8 Mbps and is derived from the cropped pixel area at 30 frames per second — a single-pass browser setting that is a target, not a guarantee of final size or visual quality. Fast motion, noise, grain, source codec, and browser encoder can all change the result. The canvas drawing step itself follows the HTML Canvas drawImage specification.
After recording finishes, the tool patches in a finite Matroska Duration so the WebM has a known length instead of streaming indefinitely. Object URLs, timers, recorder tracks, and playback are released on every exit path, including errors, replacement, stale completion, and tab unmount.
The Pixel Math for Each Instagram Format
For a 1:1 square from a 1920 × 1080 source, the math runs cleanly in whole pixels. The shortest source side is 1080, so the largest square you can fit is 1080 × 1080. Centering it horizontally gives:
X = (1920 − 1080) / 2 = 420Y = 0Width = 1080Height = 1080
Verification: X + Width = 420 + 1080 = 1500, which is less than or equal to 1920. Y + Height = 0 + 1080 = 1080, which is less than or equal to 1080. Output area = 1080 × 1080 = 1,166,400 pixels, well below the 3840 × 2160 ceiling.
For a 4:5 portrait from the same source, height stays capped at 1080 and width becomes 1080 × (4/5) = 864. Centered: X = (1920 − 864) / 2 = 528, Y = 0, Width = 864, Height = 1080. That rectangle verifies inside the source and produces a clean Instagram portrait.
For a 9:16 vertical, the 1920 × 1080 source does not contain enough vertical pixels. A 9:16 rectangle with height 1080 would need width = 1080 × (9/16) = 607.5, which is not a whole pixel and is therefore rejected by the whole-pixel rule. A 9:16 rectangle with width 1080 would need height = 1080 × (16/9) = 1920, which exceeds the source height of 1080. No single crop is geometrically possible from this source. To produce a true 9:16 file you would need to resize or letterbox the source first, then crop if you still want to trim edges.
Crop a Video to Instagram Size in Four Steps
- Choose a browser-decodable video. Pick an MP4, WebM, MOV, M4V, or Ogg file and wait for its decoded dimensions to load. An accepted extension does not guarantee codec support; decoding depends on what your browser can actually play.
- Enter the rectangle. Type the X, Y, width, and height values from your pixel math. Use whole, nonnegative numbers; width and height must each be at least two; the rectangle must stay inside every source frame; the output area must not exceed 3840 × 2160.
- Select Crop video and keep the tab open. The tool plays the source in real time, draws only the selected rectangle into the Canvas, and records the Canvas stream as WebM. A one-minute clip takes roughly one minute.
- Download and review the WebM. Watch the full output before deleting the original. Confirm the crop is centered where you intended, confirm whether audio is present, and confirm the file plays correctly in the destination app.
Limits That Can Stop the Crop Before It Starts
- File size: positive files up to 500 MiB.
- Decoded duration: more than zero and at most five minutes.
- Source dimensions: no side above 4096 pixels and no source area above 3840 × 2160.
- Output area: width × height must not exceed 3840 × 2160.
- Coordinate rules: untrimmed nonnegative whole pixels only; width and height of at least two; X + width and Y + height must stay inside the decoded source. Invalid rectangles fail without shifting, clipping, rounding, or producing a partial file.
- Output format: WebM with VP9, VP8, or generic WebM. Not MP4.
- Audio: included only if the browser exposes a capturable track through media capture. Support varies, and the source may play audibly during real-time processing, so always verify sound in the final result.
- Lost on crop: subtitles, chapters, attachments, rotation tags, HDR signaling, color metadata, and most container features.
- Rectangle behavior: one fixed rectangle applied to every frame; the tool does not track a moving subject or change the rectangle over time.
When Cropping Alone Is Not Enough
Cropping solves a specific problem: removing unwanted edges so the visible frame matches Instagram's aspect ratio. It does not solve every problem in the same step. If your source is 16:9 and your target is 9:16, the math simply does not fit, and the right sequence is to resize or letterbox the source first, then crop if needed — see the Instagram Reels format and resize guide for that workflow. If you only need a portion of the timeline rather than a portion of the frame, that is a trim task, not a crop. And if your file is too large to upload comfortably, compress it before cropping so the WebM encode stays within any size budget you have.
For the original Instagram sizing problem — matching the Feed, Story, or Reels rectangle from a source whose dimensions permit the crop — entering the right X, Y, width, and height into the Video Cropper and letting the browser do the recording is the most direct local path. Keep the original until you have watched the entire output and confirmed the crop, the audio, and the playback in the destination player.