画像リサイズ

Resize image dimensions in a few clicks

Use this page to resize image files to an exact width and height in pixels. It's the fix for upload boxes that say "image too large", social posts that get cropped badly, and product photos that are far heavier than a web page needs.

You can also crop before resizing, which matters more than people expect. If a form wants a 200 × 230 pixel photo of your face, cropping away the background first gives you a sharp face instead of a tiny one surrounded by wall.

How to resize an image

Your settings apply to every image in the batch, so you can resize a whole folder of product shots in one go.

1. 1

   写真または画像をアップロード

   JPEG、PNG、WEBP、HEICまたは対応画像をアップロードエリアにドロップ、または複数ファイルを一度に選択。

2. 2

   必要なら先にクロップ

   クロップを有効にし、寸法変更前に必要な部分だけを選択。

3. 3

   新しい幅と高さを設定

   目標サイズをピクセルで入力。アスペクト比オンで一方を空にすると比例スケール。

4. 4

   リサイズしてダウンロード

   画像をリサイズを押し、処理を待ち、結果をダウンロード。アップロードにまだ大きければ後で圧縮。

Resize image in KB: 20KB, 50KB and 100KB

A file's size in kilobytes depends mostly on how many pixels it has. Halve the width and height and you remove three quarters of the pixels, which usually takes the file down by a similar amount. That's why resizing is the most reliable first step when a form asks for something like "JPG under 50 KB".

This tool sets pixel dimensions, not kilobytes. For an exact KB limit, resize here first and then fine-tune with the target size option in Compress Image.

Exam portals often state pixel limits as well as KB limits, for example a photo of 200 × 230 pixels and a signature of 140 × 60 pixels. When both are given, match the pixel size first; the KB limit usually takes care of itself.

Common sizes worth knowing

Platforms change their recommendations from time to time, so treat this as a starting point. For banners and thumbnails, choose Cover so the frame is filled edge to edge.

Contain, Cover and aspect ratio explained

Maintain aspect ratio

On by default. Type one dimension and the other follows, so a 4000 × 3000 photo resized to 1200 wide becomes 1200 × 900. Switch it off only when you deliberately want to squash or stretch the image.

Contain

The whole picture fits inside the box you set. If the shapes don't match, one side ends up shorter than the number you typed, but nothing is cut off.

Cover

The image fills your exact width and height, and the overflow is trimmed from the edges. A landscape photo resized to 1080 × 1080 with Cover loses a strip from the left and right. Transparent areas are kept for PNG, WEBP and AVIF and filled with white for JPEG.

Allow upscaling

Off by default, so a small image is never blown up by accident. Turn it on if you really need a bigger canvas, knowing the result will be softer than a genuinely high-resolution original.

Tips for sharper resized photos

• Start from the original. Resizing a photo that WhatsApp or a social app has already shrunk throws away detail twice. Use the file straight from the camera or phone gallery when you can.
• Shrink in one step. Going from 4000 pixels to 800 in a single pass looks cleaner than resizing to 2000, then 1200, then 800.
• Crop with the final shape in mind. If the slot is square, crop to a square first. You decide what stays in the frame instead of letting Cover decide for you.
• Check text and faces at 100% zoom. Thin lines, small print and eyelashes are the first things to blur. If they look mushy, choose a slightly larger size.
• Keep a copy of the full-size file. A resized image can't be scaled back up to its original sharpness, so never overwrite your only copy.

Formats, quality and privacy

The resized image keeps its original format. JPEG, WEBP and AVIF are saved at quality 85, which keeps detail without bloating the file. PNG stays lossless. HEIC photos from iPhones come back as JPEG, and an animated GIF becomes a single still frame.

Everything runs in your browser, on your own device. Images up to 250 MB are accepted, 20 at a time, and nothing is uploaded, stored or watermarked. If you want an even smaller file after resizing, you can convert the image to WEBP, which is often 25–35% lighter than JPEG at the same quality.