Photos are too big for the places they need to go. A phone photo is 4 MB, a website wants it under 200 KB, an email form caps attachments at 1 MB, and a listing page crawls when every image is full-size. The usual fix is an upload to some stranger's server — slow, and a bad idea for private photos. Our free Image Compressor does it differently: load a photo, move the quality slider, and it shows you the exact before and after file sizes before you download. Nothing is uploaded — the compression happens on your own device. This guide explains how to compress an image with it, how compression actually works, the quality settings that save the most with the least visible loss, and the limits worth knowing before you compress a photo you cannot replace.
Step one: drop a photo in. Drop an image into the box, or tap it to browse your device — JPG, PNG, WebP, GIF or BMP. The moment an image loads, the compressor produces a compressed copy at 80% quality and shows you both file sizes side by side, so you can see exactly what you save before downloading anything. Step two: move the quality slider. The preview updates live: drag it down and watch the compressed size shrink, drag it up if you want maximum fidelity. Step three: pick the output format and size. Keep the original format, or switch to JPG (smallest for photos) or WebP (smallest overall) — on photographs WebP is typically another 25–35% smaller than JPG at the same visual quality. If the file still is not small enough, set a maximum width and height to shrink oversized phone photos down to the size they will actually be displayed at. When the numbers look right, press Download Compressed Image and the file saves with "-compressed" added to its name, so your original stays untouched.
Every image format stores pixels differently, and compression means re-storing them more cheaply. Lossy compression (JPG and WebP) permanently discards detail your eye is unlikely to notice — mostly fine texture in areas of smooth colour such as skies and skin — and the quality slider controls how aggressively it discards. At 100% almost everything is kept; at 80% the discarded detail is essentially invisible in a photograph; below 60% you start to see blocky artefacts around edges and text. Lossless compression (PNG) keeps every pixel exactly and only packs the data more efficiently, which is why PNG files stay large for photographs but are the right choice for logos, screenshots and anything with sharp text. One honest detail many tools hide: re-saving a PNG as a PNG can only shrink it slightly, because the pixels are already stored losslessly. Real savings on a PNG photo come from converting it to JPG or WebP — or from reducing its dimensions. A 4,000 × 3,000 phone photo displayed at 800 pixels wide on a website carries sixteen times more pixels than anyone will ever see, so resizing is often the single biggest, safest saving available.
The table the tool page publishes is the whole decision in one place. At 90–100% quality you save only 10–30%, which suits archiving, print and professional portfolios. At 80–85% — the default sweet spot — files are typically 60–80% smaller, which suits website hero images, blog photos and listings. At 70–75% you save 75–85%, which suits thumbnails, gallery grids, social uploads and email attachments. At 50–65% you save 85–92%, which suits previews and placeholders where a little softness is acceptable. Below 50% you save 92% or more, but artefacts become obvious and it is rarely worth it. The slider has no effect on PNG output, because PNG is lossless — if you want a smaller PNG, convert it to WebP (which supports transparency and is usually far smaller) or to JPG if it is a photograph without transparency. For most website photographs, 80% quality in WebP (or JPG as a fallback) is the sweet spot: files are typically 60–80% smaller than the original with no difference a visitor can see. Also resize to the largest size the image will actually be displayed at — a hero image rarely needs to be wider than 1,920 pixels, and content images are usually fine at 1,200 pixels wide.
Take a 4.2 MB phone photo at 4,032 × 3,024 pixels — the kind of file every phone produces by default. Compressed as a JPG at 80% quality it lands near 900 KB with no visible change on a screen. The same file as WebP at 80% is closer to 620 KB. Add a maximum dimension of 1,600 pixels — still sharper than most laptop screens — and the WebP drops under 200 KB, a 95% saving, because the resize discards pixels instead of detail. That is the combination most websites actually want: the right format, the 80% sweet spot, and a maximum dimension matched to where the image will be shown. If you are working with a batch of iPhone photos instead, our HEIC guide covers converting them first, and our image resizer guide covers exact pixel dimensions and social presets when the size itself is the problem rather than the file weight.
Compressing at 100% and wondering why nothing shrank. At 100% quality almost everything is kept — the saving comes from the slider, and 80% is where it starts. Converting a small JPG to PNG. PNG is lossless, so the "compressed" file can come out larger than the original — the result box tells you honestly when the new file is larger and suggests the fix: lower the quality slider, choose WebP, or set a maximum dimension. Compressing an already-compressed JPG again and again. Lossy artefacts compound, so each re-save costs a little quality; work from the original camera file whenever you can, and treat each compressed output as a finished copy, not a new master. Forgetting to resize oversized phone photos. A 4,000-pixel-wide photo shown at 800 pixels carries sixteen times more pixels than anyone will see — resizing is often the biggest, safest saving available. Sending WebP to old software. WebP is supported by every modern browser, but a few older applications still cannot open it — if you are sending a file to someone else's older software, JPG is the safest choice.
The honest limits are four. First, compression is a one-way door: detail discarded by a lossy save cannot be recovered, so always keep your original file — this tool never alters it. Second, re-encoding strips the EXIF metadata cameras embed in photos — GPS coordinates, device model and timestamps — which is a quiet privacy win when you share images publicly, though you should keep the untouched original if you rely on that data for organising your library. Third, animated GIFs are flattened to their first frame, because the browser canvas does not preserve animation. Fourth, extremely large images (for example 100-megapixel scans) may exceed your browser's memory on low-end phones; if a file fails to load, resize it first or try on a laptop. Within those limits, the tool does one job completely: the file you download is smaller by an amount you chose, in the format you chose, at the size you chose — with the exact before and after sizes shown before you commit. Two companion guides cover the neighbouring jobs: our image resizer guide handles exact pixel dimensions and social presets, and our image upscaler guide covers the opposite direction — making a small image bigger with AI.
Resize any photo to exact pixels, by percentage or with one-tap social presets — Instagram 1080×1080, YouTube 1280×720 — and download it as JPG, PNG or WebP. Free, private, in your browser.
Batch-convert up to 20 iPhone photos at once — JPG at 85% vs lossless PNG (61 MB vs 148 MB on the same 20 photos), and why the first conversion takes longer.
2x vs 4x explained, the 1200×900 to 4800×3600 print example (16×12 inches at 300 DPI), and the honest limits — blur, tiny text and waxy textures included.