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Aspect Ratio Crop Online

Browser-side — no upload
Last verified May 2026 — runs in your browser

Aspect Ratio Crop — Auto-Centred to 5 Platform-Standard Ratios via WHATWG Canvas drawImage Sub-Rectangle Extraction

Crop any image to one of 5 platform-standard aspect ratios with automatic centre-crop computing the largest possible rectangle that fits the target ratio inside the source: 1:1 (Instagram square posts, profile avatars, app icons), 4:3 (NTSC/PAL/SECAM standard-definition television per ITU-R BT.601 ratified 1982, also classic tablet displays + printer photo formats), 16:9 (HDTV widescreen per ITU-R Rec. 709 approved by CCIR in 1989, first official release 1990, BT.709-1 November 1993 — YouTube videos, modern 1080p/4K monitors, TVs), 3:2 (35mm still-photography ratio originated by Oskar Barnack's Leica I in 1925 at Leipzig Fair via the 24×36mm full-frame format derived from two horizontally-stitched 18×24mm cine frames, still the native ratio of full-frame digital SLR/mirrorless sensors), and 9:16 (vertical / portrait — TikTok, Instagram Stories + Reels, YouTube Shorts, mobile-first vertical video formats). The conversion runs locally via WHATWG Canvas drawImage's 9-argument source-rectangle extraction form (`drawImage(source, sx, sy, sw, sh, dx, dy, dw, dh)` per html.spec.whatwg.org/#dom-context-2d-drawimage) — the largest target-ratio rectangle is computed and centred on the source, then those pixels are extracted to a fresh canvas at native resolution. Output format matches source: PNG sources stay PNG with full RGBA alpha; JPG sources output JPG at quality 0.92 (re-encoded via canvas.toBlob with Annex K quantisation per ITU-T T.81). Files never leave the device.

Related: Crop Image Circle Crop Social Media Resizer Resize Image Image Grid Splitter Image Upscaler

How to crop to an aspect ratio

  1. Drop your image onto the tool or click to browse. The browser's built-in decoder loads the source at native dimensions.
  2. Pick the target aspect ratio: 1:1 (square), 4:3 (television classic), 16:9 (HDTV widescreen), 3:2 (35mm photo), or 9:16 (vertical for mobile-first video). The auto-centre algorithm computes the largest target-ratio rectangle fitting inside the source.
  3. Review the centred crop preview. The crop is computed at native source resolution — no scaling is applied; only the pixels outside the target-ratio rectangle are discarded.
  4. Click Download to save the cropped image. The output preserves source format (PNG with RGBA, or JPG at quality 0.92). The original file stays on disk untouched — files never leave the device.

Common use cases

  • Preparing 1:1 square thumbnails for Instagram grid posts and profile avatars where the platform's automatic crop is rarely where you want the subject.
  • Cutting wide-angle landscape photos to 16:9 for YouTube thumbnails, hero banners on landing pages, or modern monitor wallpapers.
  • Trimming DSLR/mirrorless full-frame 3:2 shots to fit photo-lab prints expecting that classic 35mm ratio.
  • Converting horizontal photos to 9:16 vertical crops for TikTok, Instagram Stories + Reels, YouTube Shorts, or Snapchat where horizontal media renders as small letterboxed boxes.
  • Producing 4:3 crops for tablet display contexts (iPad Air/Pro), classic 4×6 / 5×7 photo prints, or NTSC-era video projects that maintain the legacy aspect.

Frequently asked questions

Will I lose parts of the image when cropping?

Yes — any pixel outside the centred target-ratio rectangle is discarded. The auto-centre algorithm picks the largest target-ratio rectangle that fits inside the source dimensions, centred horizontally and vertically. For off-centre subjects, run the source through the crop-image tool first to position the subject in the geometric centre of the source, then apply aspect-ratio-crop.

Why these five aspect ratio presets?

These five cover the vast majority of social-media, print, and video aspect ratio use cases as of 2026. 1:1 (Instagram square + app icons + profile avatars); 4:3 (NTSC/PAL television per ITU-R BT.601 1982 + tablet displays + printer-friendly photo formats); 16:9 (HDTV per ITU-R Rec. 709 1989 + YouTube + modern monitors); 3:2 (35mm photography per Leica 1925 + full-frame digital sensors); 9:16 (vertical for TikTok + Instagram Stories/Reels + YouTube Shorts). Custom arbitrary ratios are accessible via the crop-image tool's manual W×H input fields.

Does the tool add padding if my image's aspect ratio doesn't match?

No. The aspect-ratio-crop tool exclusively crops (removes pixels outside the target rectangle); it never adds padding pixels. If the source's aspect ratio doesn't match the target, the auto-centre algorithm picks the largest target-ratio rectangle that fits inside the source — pixels outside that rectangle are discarded. To add padding (letterbox/pillarbox) instead of cropping, use a layout-aware tool like social-media-resizer.

What output format does the tool produce?

The output preserves source format: PNG sources output PNG (8-bit alpha per RGBA pixel preserved byte-exactly per W3C PNG 2nd Edition 10 November 2003 / ISO/IEC 15948:2004); JPG sources output JPG re-encoded via canvas.toBlob at quality 0.92 (ITU-T T.81 Annex K perceptual quantisation, approximately 1-2% perceptually invisible additional loss versus the source). Non-PNG, non-JPG sources are encoded as JPG quality 0.92 by default.

Is my image uploaded anywhere?

No. The decode + auto-centre computation + Canvas drawImage 9-argument source-rectangle extraction + toBlob re-encoding all run client-side via WHATWG Canvas. DevTools Network tab shows zero upload requests during conversion.

5 aspect ratio presets + auto-centred max-fit crop + WHATWG Canvas drawImage 9-argument extraction

The aspect-ratio-crop tool exposes 5 platform-standard ratios as preset options: 1:1 (the universal square — Instagram square posts and profile avatars, app icon source masters), 4:3 (the NTSC/PAL/SECAM standard-definition television aspect ratio per ITU-R BT.601 ratified by the CCIR in 1982 — the standard TV aspect for nearly 70 years until HDTV's 16:9 displaced it; still used for tablet displays, classic camera SLRs, and printer-friendly 4×6/5×7 photo formats), 16:9 (HDTV widescreen per ITU-R Rec. 709 — approved by the CCIR in 1989 as 'Recommendation XA/11 MOD F', first official release 1990, renamed to ITU-R BT.709 when the CCIR became ITU-R in 1992, BT.709-1 November 1993 — the modern HDTV/UHDTV widescreen ratio universally used for YouTube videos, 1080p/4K monitors, modern TVs), 3:2 (the 35mm still-photography ratio originated by Oskar Barnack at Ernst Leitz Wetzlar — the Ur-Leica prototype 1913, the commercial Leica I released at the Leipzig Fair 1925 — via the 24×36mm full-frame format derived from stitching two 18×24mm cine frames horizontally; the native ratio of every full-frame digital SLR/mirrorless sensor through 2026), and 9:16 (the inverse of 16:9, i.e. portrait-orientation widescreen — used by TikTok, Instagram Stories + Reels, YouTube Shorts, Snapchat, and most mobile-first vertical video formats since smartphone use overtook desktop ~2017). The auto-centre algorithm computes the largest rectangle of the target aspect ratio that fits inside the source dimensions: if the source's width/height ratio exceeds the target, the crop uses full source height and computes width = height × target_ratio (centred horizontally); otherwise the crop uses full source width and computes height = width / target_ratio (centred vertically). Centring offsets are then `ox = (sourceWidth - cropWidth) / 2`, `oy = (sourceHeight - cropHeight) / 2`. The crop is extracted via WHATWG Canvas drawImage's 9-argument source-rectangle form at native resolution. Output preserves source format: PNG → PNG with RGBA; JPG → JPG quality 0.92 via canvas.toBlob (ITU-T T.81 Annex K perceptual quantisation).

  • Five platform-standard aspect ratio presets: 1:1 (square) + 4:3 (NTSC/PAL BT.601) + 16:9 (HDTV Rec. 709) + 3:2 (35mm Leica) + 9:16 (TikTok/Stories vertical)
  • Auto-centred max-fit crop algorithm: the largest target-ratio rectangle that fits inside the source, centred on the source
  • Live preview of the centred crop area at native resolution before download
  • Output preserves source format: PNG sources stay PNG with RGBA alpha; JPG sources output JPG at quality 0.92 (ITU-T T.81 Annex K)
  • WHATWG Canvas drawImage 9-argument source-rectangle extraction at native pixel resolution (no scaling, no resampling)
  • Pixels inside the centred crop rectangle preserved 1:1; pixels outside the rectangle discarded (lossless from the source pixels)
  • Browser-side via WHATWG Canvas drawImage + HTMLCanvasElement.toBlob — no upload
  • Operates in sRGB (IEC 61966-2-1:1999); source images without an embedded ICC profile are interpreted as sRGB

Free. No signup. No file uploads. Ads via AdSense (consent required).

Sources (10)
  • WHATWG (live). HTML Living Standard — Canvas 2D Context: drawImage() 9-argument source-rectangle extraction form. html.spec.whatwg.org/#dom-context-2d-drawimage — the auto-centred crop pipeline core: the largest target-ratio rectangle that fits inside the source is computed (cw = sourceWidth or sourceHeight × ratio depending on direction; centring offsets ox = (sourceWidth - cw)/2, oy = (sourceHeight - ch)/2), then extracted via drawImage's 9-argument form.
  • International Telecommunication Union (ITU-R, formerly CCIR) (1982). ITU-R BT.601 — Studio encoding parameters of digital television for standard 4:3 and wide screen 16:9 aspect ratios. itu.int/rec/R-REC-BT.601 — the 4:3 NTSC/PAL/SECAM standard-definition television aspect ratio, ratified by the CCIR in 1982; the standard TV aspect for nearly 70 years before HDTV's 16:9 displaced it in the mid-2000s.
  • International Telecommunication Union (ITU-R, formerly CCIR) (1990). ITU-R Rec. 709 / BT.709 — HDTV signal characteristics + 16:9 aspect ratio. itu.int/rec/R-REC-BT.709 — the 16:9 HDTV widescreen aspect ratio standard, approved by the CCIR 1989 as 'Recommendation XA/11 MOD F', first official release 1990, renamed to ITU-R BT.709 when the CCIR became ITU-R in 1992, BT.709-1 November 1993 — the modern HDTV/UHDTV widescreen ratio for YouTube, monitors, TVs.
  • Barnack, O. (Ernst Leitz Wetzlar) (1925). Leica I — 35mm full-frame 24×36mm format + 3:2 aspect ratio origin. leica-camera.com/en-US/photography/100-years/the-history-of-the-leica-I — the 35mm still-photography 3:2 aspect ratio origin: Oskar Barnack's Leica I commercial release at the Leipzig Spring Fair 1925 (Ur-Leica prototype 1913), establishing the 24×36mm full-frame format derived from two stitched 18×24mm cine frames; the native ratio of full-frame digital SLR/mirrorless sensors through 2026.
  • Industry convention (TikTok / Instagram / YouTube) (2017). 9:16 vertical aspect ratio for mobile-first short-form video. tiktok.com/business/en + instagram.com (Stories, Reels) + youtube.com/shorts — the 9:16 inverse-of-16:9 portrait-orientation aspect ratio became the dominant short-form video format after smartphone use overtook desktop ~2017; used by TikTok (launched internationally 2017), Instagram Stories (2016), Instagram Reels (2020), YouTube Shorts (2021), Snapchat Stories (2013).
  • WHATWG (live). HTML Living Standard — HTMLImageElement (browser-native raster decoding). html.spec.whatwg.org/#htmlimageelement — universal browser entry point for raster format decode into Canvas drawImage.
  • ITU-T (CCITT) Study Group VIII & ISO/IEC JTC 1/SC 29/WG 10 (JPEG) (1992). Information technology — Digital compression and coding of continuous-tone still images: Requirements and guidelines. ITU-T Recommendation T.81 (18 September 1992) / ISO/IEC 10918-1:1994 — JPEG baseline DCT bitstream; Annex K quantisation tables scale by the canvas.toBlob quality argument (0.92 in this tool's JPG output path).
  • Hamilton, E. (C-Cube Microsystems) (1992). JPEG File Interchange Format (JFIF) Version 1.02. 1 September 1992 — JPEG container format; APP0 marker, density units, thumbnail handling. Output via canvas.toBlob('image/jpeg') ships JFIF v1.02 by default.
  • W3C (PNG Working Group) (2003). Portable Network Graphics (PNG) Specification (Second Edition). W3C Recommendation 10 November 2003 / ISO/IEC 15948:2004 — PNG output format for sources with alpha; preserves 8-bit alpha per RGBA pixel byte-exactly through canvas.toBlob('image/png').
  • International Electrotechnical Commission (IEC) (1999). Multimedia systems and equipment — Colour measurement and management — Part 2-1: Default RGB colour space — sRGB. IEC 61966-2-1:1999 — default 8-bit RGB colour space the Canvas 2D path operates in.

These are the W3C, ISO/IEC, ITU-T, and IETF specifications the tool implements or builds on. Locate them on w3.org, iso.org, itu.int, or datatracker.ietf.org.

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