What makes an image file so large?
Three things decide the size of an image file: how many pixels it has, how those pixels are stored, and what extra data rides along. A 12-megapixel phone photo is about 4000 by 3000 pixels and weighs 3 to 5 MB as a JPG. A 48-megapixel shot or a 600 dpi scan can be 10 to 25 MB. None of that detail is visible on a screen 1920 pixels wide, or in a form that shows the picture 400 pixels wide.
The format is the second factor. PNG stores every pixel exactly, which is perfect for a logo but wasteful for a photo, where the same picture can be five to ten times larger as a PNG than as a JPG. A photo someone exported as PNG is the most common reason a file is too large to upload.
The third factor is metadata. Every camera photo carries an EXIF block with the date, camera model, lens settings and often GPS coordinates. That adds a few kilobytes to a few hundred, which matters when a form says 100 KB.
Resize first, then compress
This is the step most people skip, and it has the biggest effect. Compressing a 4000-pixel-wide photo harder and harder leaves you with a large, ugly file. Resizing it to 1600 pixels wide first drops it to roughly a sixth of the pixels, so the file shrinks to about a sixth of the size before you touch the quality setting.
Pick the width from where the picture will be used. For an email attachment, 1600 to 2000 pixels on the long side is plenty. For a web page, match the width of the slot the image fills, doubled for high-resolution screens, so typically 1200 to 1600 pixels. For a profile picture or an ID photo, 600 to 800 pixels is more than the form will ever display.
Always resize a copy and keep the original. For the step-by-step, see how to resize an image.
JPG, PNG or WebP: which format makes the smallest file?
JPG is the right choice for photos and anything with smooth color gradients. It is lossy, meaning it discards detail your eye is unlikely to notice, which is exactly why it is small. Every device and upload form accepts it.
PNG is the right choice for screenshots with text, logos, charts and anything with a transparent background. It is lossless, so text stays crisp. Use it for photos only if transparency is required.
WebP, the format Google designed for the web, does both jobs and is 25 to 35 percent smaller than JPG at the same visible quality. It is the best choice for images on your own website and a poor one for email and forms, which often reject it. If you are stuck with a WebP, see how to convert WebP to PNG or JPG.
A practical rule: photo going to a person or a form, JPG. Screenshot or logo, PNG. Image on a web page you control, WebP. HEIC from an iPhone, convert to JPG first.
What does 80 percent JPG quality actually look like?
JPG quality is a number from 1 to 100, and the relationship with file size is not linear. Going from 100 to 90 often halves the file with no change you can see. Going from 90 to 80 takes off another 30 to 40 percent, and side by side with the original most people cannot tell which is which. That is why 80 is the standard default for web images.
Below 70, artifacts start to show: faint blocks in smooth areas such as skies and skin, and a slight smear around sharp edges like text. At 50 the picture is clearly degraded. For something a person will look at, stay at 75 or above.
Two warnings. Quality numbers are not comparable across programs, so judge by eye at 100 percent zoom. And never compress a JPG that has already been compressed several times, because the artifacts stack up with each save. Start from the best version you have, resize it, and compress once.
How to compress an image online, including a whole batch
An online compressor is the quickest route for more than a couple of images, or on a Chromebook or a phone. Compress image on DocGopher takes JPG, PNG, WEBP and iPhone HEIC photos and makes them much smaller for email, web and upload. It is free, needs no sign-up and adds no watermark. Drop up to 50 images per batch, up to 300 MB in total; files are processed in memory and deleted after 30 minutes.
If you only have photos, the Compress JPG page does the same job and keeps the result to JPG. For a PNG that is really a photo, converting it to JPG first with the image converter will shrink it far more than any PNG compression can.
- Open the Compress image page in your browser, on a computer or on your phone.
- Drag your images onto the page or pick them from a folder or the camera roll.
- Start the compression and wait for the batch to finish.
- Download the result. Several files arrive as one ZIP. Check one or two at full size and compare the new sizes against the limit you need to meet.
How to compress an image with what you already have
You do not always need a separate tool. Mail, Photos and the phone share sheet have a shrink option built in, and for a single photo going to one person they are the fastest path.
Mail on a Mac: attach the photo, then look at the bottom right of the message window for an Image Size menu. Small is around 320 pixels wide, Medium around 640 and Large around 1280. Medium or Large is right for almost every email. On the iPhone, Mail asks the same question when you tap Send and shows the resulting file size next to each option.
Windows Photos: open the image, click the three dots in the top bar, and choose Resize image. Pick a preset or type a pixel width. For a JPG there is also a quality slider; 80 is a good value. Save as a copy so the original stays intact. Paint can also save as JPEG, but with no control over quality.
Phones: on iPhone, Messages and Mail shrink photos automatically or ask you; the Photos app itself has no size setting. On Android, Samsung's Gallery has Resize image in the editor's menu, and apps such as WhatsApp compress every photo on their own. Gmail on both platforms does not resize, so an attachment goes at full size unless you shrink it first.
What file size should you aim for?
Email: keep each image under 1 MB and the whole message under 10 MB, since corporate mail servers often stop there. A 1600-pixel JPG at 80 percent quality lands between 300 and 600 KB, so three or four photos per email is comfortable.
Web pages: aim for under 200 KB for a large hero image and under 100 KB for everything else. Page speed tools flag images above that, and on a phone connection a 2 MB photo visibly slows the page.
Forms: read the limit and work backward. A form that demands 100 KB usually also specifies pixel dimensions, often something like 600 by 600 for an ID photo. Resize to exactly those dimensions, save as JPG, and the file will typically be 40 to 80 KB. A 2 MB limit is generous: a 2000-pixel JPG at 85 percent fits easily. If a form says 500 KB and still rejects your file, drop the quality to 70 before you shrink the pixels further, because dimensions are often checked too.
Strip the hidden metadata before you share
Metadata removal gives you a few kilobytes back, but the real reason to do it is privacy. A photo taken with location services on carries the GPS coordinates of where you stood, the exact date and time and your phone model. Social networks strip this when you upload. Email, cloud links and your own website do not.
On an iPhone, tap Share on a photo, tap Options at the top of the share sheet and turn off Location. On Windows, right-click the file, choose Properties, Details, and click Remove Properties and Personal Information. Online, Remove EXIF deletes the camera details, date and GPS location from a batch of photos in one pass. Most compressors also drop the EXIF block, but check the file properties afterward if it matters.
Frequently asked questions
How do I compress an image without losing quality?
Resize the image to the pixel width it will be shown at, then save it as a JPG at 80 to 85 percent quality. At that setting the difference from the original is not visible at normal viewing size. Compress once from the best version you have.
How do I compress a JPEG to 100 KB?
Resize it first to the dimensions the form asks for, usually a few hundred pixels on each side, then save as JPG at 80 percent quality. A 600 by 600 pixel JPG is typically 40 to 80 KB. If it is still over, lower the quality to 70, then 60, checking the size each time.
Why does my image say it is too large to upload?
The file is above the site's size limit, often 2 MB, 1 MB or 500 KB. Camera photos are 3 to 25 MB and PNG photos are larger still. Resize the picture to around 1600 pixels on the long side and save it as JPG.
Which format gives the smallest image file?
For photos, WebP is smallest, followed by JPG. For screenshots, logos and anything with a transparent background, PNG is the right choice even though it is larger. Use JPG for email and forms because every service accepts it, and WebP for images on your own website.
How do I reduce a photo's size on my phone before emailing it?
On an iPhone, attach the photo in Mail and tap Send; Mail offers Small, Medium, Large or Actual Size. On Android, use Resize in the Gallery editor if your phone has it, or run the photo through a free online compressor first. Gmail does not shrink attachments on its own.