图片尺寸计算器 — 图像大小和宽高比

Open the Photo Dimensions Calculator — Free Image Size & Aspect Ratio in your browser and click the blue "Choose file" button or drag your image onto the drop area; you can also paste an image from the clipboard into the input field. The tool immediately reads the file and displays its pixel dimensions (e.g., 4000 x 3000 px), file type, and orientation, then shows a simplified aspect ratio (e.g., 4:3) and the greatest-common-divisor ratio. To resize, enter the new width or height in the fields, pick units (pixels, inches, cm), choose whether to "Maintain aspect ratio" and press the "Calculate" or "Resize image" button to get exact output dimensions and the download link.

Photo Dimensions Calculator accepts JPG/JPEG, PNG, WebP, GIF (static), BMP, TIFF and HEIC input files; exported downloads can be saved as JPG or PNG depending on your choice. The tool processes single files up to roughly 50 MB comfortably in desktop Chrome or Firefox; batch processing is practical up to 10 files at once though mobile browsers may hit memory limits earlier. Very large TIFF stacks or animated GIFs are handled differently—animated GIFs show only the first frame for dimension calculations—so for multi-frame files export a flattened PNG/JPG first.

After loading a picture into Photo Dimensions Calculator, the interface shows the exact pixel dimensions and immediately computes the reduced aspect ratio using GCD (greatest common divisor), presenting it as a clean ratio such as 4:3 or 16:9. There is an "Aspect ratio" panel that also lists common presets (1:1, 3:2, 16:9, 5:4) and a "Lock aspect ratio" checkbox you can toggle before resizing so the other side auto-updates. The tool also provides a suggested crop and a preview thumbnail so you can see how a chosen ratio will affect framing before you click "Resize" or "Crop".

Yes — Photo Dimensions Calculator performs all calculations and resizing in your browser using the HTML5 canvas API, so files are not uploaded to a remote server by default. After you click "Choose file" the image stays in your local browser session, operations complete locally, and clicking "Download" writes the resized file to your device; nothing is sent unless you explicitly use a share button. Note that very large images can still trigger memory limits in mobile Safari or older browsers, so for files near the 50 MB range use desktop Chrome or Firefox to avoid crashes.

Load your image or manually enter pixel dimensions into Photo Dimensions Calculator, then open the "Print size" section and set the target resolution (DPI/PPI) — common choices are 72 for screens, 150 for posters, 300 for high-quality photo prints, and 600 for fine art prints. The tool will compute physical print dimensions using the formula width (in) = pixels ÷ DPI and height (in) = pixels ÷ DPI — for example, a 3000 x 2400 px image at 300 DPI results in a 10.00 x 8.00 inch print. The calculator also shows metric values in cm, reminds you to add bleed if needed (default 3 mm) and warns when the effective DPI drops below recommended print quality levels.

When you downscale in the Photo Dimensions Calculator the browser canvas resamples pixels using a high-quality interpolation (close to bicubic), which preserves detail better than nearest-neighbor but still discards fine texture when reducing a lot. You can choose output file type and JPG quality (a slider from 50 to 95 is available; default 90), so lower JPG quality will reduce file size at the cost of compression artifacts; saving as PNG preserves pixel-perfect results for graphics but produces larger files. If you need advanced sharpening or proprietary resampling (e.g., Photoshop's "Preserve Details 2.0") use a desktop editor after resizing; the calculator is best for quick, local resizes and accurate dimension calculations.

Those errors usually mean the file is too large for the browser's available memory or a format that the browser can't decode; Photo Dimensions Calculator works best with files under ~50 MB in desktop Chrome/Firefox and under ~10–20 MB on mobile Safari. Fixes include: open the file on desktop Chrome/Firefox, reduce image size in another app before uploading, convert HEIC to JPG if Safari can't decode it, or use the tool's "Compress first" option to lower dimensions. Also try closing other heavy tabs, enabling 64-bit browser builds, or splitting large multi-page TIFFs into single images to avoid memory spikes.

The tool allows batch processing of up to 10 images simultaneously using the "Add files" button; each file is processed locally in the browser and you can set the same target dimensions or DPI for the whole batch. Once processing finishes you can use the "Download All" button to get a single ZIP with all resized images, but be aware that zipping large batches can be memory-intensive on mobile. For very large automated batches or server-side workflows, desktop apps or command-line tools (ImageMagick) are still the better option.

Yes — Photo Dimensions Calculator exposes a DPI/PPI field where you can enter values like 72, 150, 300, or 600 to calculate physical print dimensions from pixels; entering 300 DPI for a 3000 px image gives a 10-inch output. There is also a "Resample" checkbox: if unchecked, changing DPI only alters the printed size metadata without changing pixel dimensions; checking "Resample" will actually scale pixels to match the intended output size. Remember that changing DPI without resampling doesn't change image detail — printers interpret PPI to determine dot placement but the underlying pixels remain the same.

Photo Dimensions Calculator is a zero-install, free browser tool that quickly shows exact pixel dimensions, aspect ratios, and basic resizes with local processing and no signup; it’s ideal for quick checks and one-off adjustments. Photoshop/Lightroom provide advanced resampling algorithms (Bicubic Smoother/Preserve Details), color profile management (ICC), smart sharpen, automated batch actions and non-destructive workflows, so they’re better for professional retouching and print prepress. If you only need to calculate print sizes, convert pixels, or resize a handful of images without installing software, Photo Dimensions Calculator is faster; for color-critical or heavy batch work use desktop apps.

Yes — Photo Dimensions Calculator has a "Paste or URL" field where you can paste an image URL or press Ctrl/Cmd+V to paste an image from your clipboard; the tool will fetch the image and display pixel dimensions and aspect ratio. Note that for remote URLs the server must allow cross-origin requests (CORS); if the image won't load due to CORS restrictions the tool will show an error and you'll need to download the image and upload it manually. Pasting from screenshots or copying images directly from most apps works fine in Chrome and Firefox on desktop.

Mobile Safari on iOS may hand HEIC files to the page differently and will often convert them to JPG under the hood, which can cause color/profile changes or memory pressure with large HEICs; for large files use desktop Chrome/Firefox. iOS has stricter memory limits so images that work on desktop may trigger "Out of memory" on iPhones — reduce pixel dimensions or process on a desktop machine. Chrome tends to allow multiple file downloads but may block automatic downloads behind a permission popup; if "Download All" doesn't work, allow downloads for the site in Chrome's site settings or download files individually.