Image File Size Estimator
Estimate output size for different image formats and quality levels
Image File Size Estimator — what it does
Try an output format and quality setting against your image and see the estimated file size and the change from the original before committing to it. It converts the usual guesswork — export, check, undo, export again — into one comparison you can read directly.
When this tool helps
- Finding the quality level that lands a photo just under an upload size limit.
- Comparing JPG against WebP for the same picture to see what the format change is actually worth.
- Budgeting page weight when a layout calls for a dozen images.
How to use it
- Choose the image.
- Select an output format.
- Adjust the output quality.
- Read the estimated size and change, then download if it fits.
Accuracy, limits, and good practice
- Compression efficiency depends on content: a flat graphic shrinks dramatically while a detailed landscape resists at any quality.
- If quality alone cannot get you under a limit, reduce dimensions — fewer pixels beats harder compression for both size and appearance.
- Estimates come from actually encoding the image, so what you see is what the downloaded file will be.
Frequently asked questions
Why is my PNG barely changing?
PNG is lossless, so the quality control has little to do. Photographs need JPG or WebP for real reductions.
Which format wins most often?
WebP, typically 25 to 35 percent smaller than JPG at matching visual quality, and supported by every current browser.
Does the estimate include metadata?
The re-encoded output carries no EXIF, which is part of why the result can be smaller than the source at the same quality.
Related tools on this site
- Photo ID Sheet Generator — Arrange repeated ID photos on an A4 or Letter sheet
- Circular Avatar Crop — Crop an image into a circular PNG avatar
- Image Color Picker — Click an image to identify HEX and RGB colors
Everything above runs inside this page. Image File Size Estimator needs no account, no upload, and no server round trip — close the tab and nothing is left behind.
圖片檔案大小估算能做什麼
在真正決定之前，先用不同輸出格式與品質試算，看看估計檔案大小以及相對原檔的變化。它把「匯出、檢查、復原、再匯出」的猜謎過程，變成一次可以直接讀懂的比較。
什麼時候用得上
- 找出讓照片剛好落在上傳容量限制以下的品質設定。
- 用同一張圖比較 JPG 與 WebP，看換格式究竟值多少。
- 版面要放十幾張圖時，先估算頁面重量預算。
使用步驟
- 選擇圖片。
- 選擇輸出格式。
- 調整輸出品質。
- 查看估計大小與變化，符合就下載。
精確度、限制與實務建議
- 壓縮效率取決於內容：平面圖形會大幅縮小，細節豐富的風景照則無論品質怎麼調都很難壓。
- 若光靠品質壓不到限制以下，就縮尺寸——就大小與觀感而言，減少像素都勝過硬壓。
- 估算是實際編碼後得到的，所以看到的就是下載檔案的大小。
常見問題
為什麼我的 PNG 幾乎沒變？
PNG 是無損格式，品質設定作用有限。照片要真的變小得用 JPG 或 WebP。
哪種格式最常勝出？
WebP。同等視覺品質下通常比 JPG 小 25% 至 35%，且目前所有瀏覽器都支援。
估算有包含中繼資料嗎？
重新編碼後的輸出不含 EXIF，這也是同樣品質下結果可能小於原檔的原因之一。
本站相關工具
以上步驟全部在這個頁面內完成，圖片檔案大小估算 不需要註冊、不上傳檔案、也不經過伺服器，關閉分頁後不會留下任何資料。