jarvisbox

Bulk Image Resizer

Resize hundreds of photos at once — set width, height, or scale % — keeping aspect ratio. No upload, instant ZIP download.

100% client-side · no upload. Images are resized in your browser using the Canvas API. Files never leave your device.
Resize settings
Quick presets:
Features: Aspect ratio preserved Batch processing ZIP download JPEG · WebP · PNG output

How to use

  1. 1. Drop one or more images onto the upload zone — JPEG, PNG, WebP, or AVIF are all accepted.
  2. 2. Choose a mode: By width (most common), By height, Fit within square, or Scale by percentage.
  3. 3. Enter a target size or use a quick preset — 1080, 1280, 1920, or 4K (3840).
  4. 4. Select an output format: JPEG for photos, WebP for web assets, or PNG for lossless.
  5. 5. Click Resize all, then download individual files or click Download ZIP for all results at once.

Why bulk resize images before sharing or uploading?

Photos from modern smartphones are typically 4000–8000 px wide and 3–12 MB each. Most use cases — websites, email, social media, presentations — display images at a fraction of that resolution. Uploading full-size originals wastes bandwidth, slows load times, and can exceed email attachment limits or CMS upload quotas.

Resizing a batch of 50 photos to 1920 px wide before uploading reduces total file size by 80–95% with no visible quality difference on any screen. This tool processes all your images at once in the browser — no upload, no server queue, no file count cap.

Resize modes explained

By width (default): each image is scaled so its width equals the target value. Height is calculated automatically to preserve the original aspect ratio. A landscape 16:9 photo resized to 1920 px wide becomes 1920×1080 px; a portrait 4:3 photo resized to 1920 px wide becomes 1920×2560 px.

By height: useful when you need a consistent height — for example, all images on a horizontal scroll gallery need to be exactly 600 px tall.

Fit within square: scales each image so its longest side equals the target. A 4000×3000 px image fit to 1000 px becomes 1000×750 px; a 3000×4000 px portrait fit to 1000 px becomes 750×1000 px. No cropping, no padding — just scale to fit the bounding box.

Scale by percentage: resizes both dimensions by the given percentage. 50% halves both width and height; 200% doubles them. All aspect ratios are preserved exactly.

常見問題

Does the aspect ratio stay the same when resizing?
Yes, in "By width" and "By height" modes the other dimension is calculated proportionally from the original image, so no distortion occurs. For example, a 4000×3000 px image resized to 1920 px wide becomes 1920×1440 px. The "Fit within square" mode also preserves aspect ratio by scaling so the longest dimension reaches your target.
Does this tool upload my photos to a server?
No. All image processing happens entirely in your browser using the Canvas API. Your photos are decoded on your device, resized in memory, and downloaded directly — nothing is ever sent to a server, stored in the cloud, or accessible to anyone else.
How many images can I resize at once?
There is no hard file count limit. Images are processed one at a time sequentially in your browser tab. For large batches (100+ files), allow extra time as each image must be decoded, drawn to a canvas at the new dimensions, and re-encoded. Modern devices typically process 10–20 images per second at typical web resolutions.
Which output formats are supported?
JPEG (best for photos, smallest file size), WebP (modern format, 20–35% smaller than JPEG at the same quality), and PNG (lossless, larger files but no compression artifacts). JPEG and WebP support a quality slider from 1–100; PNG is always lossless and ignores the quality setting.
Will upscaling make my images look better?
No — upscaling interpolates new pixels that were not in the original, which cannot add real detail. If you set a target width larger than the original image, the output will look the same or slightly softer than the source. This tool does not block upscaling (some workflows require it), but downscaling is where you see the most benefit.
Does it work on iPhone and Android?
Yes. The tool works in any modern browser: Safari on iPhone (iOS 15+), Chrome on Android, and desktop browsers. Tap the upload zone to open your photo library. The ZIP download uses the standard browser download API supported by all modern mobile browsers.

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