Free Online DICOM Viewer

View DICOM Files in Your Browser

Open and view supported DICOM files with our free online DICOM viewer. Load medical images from your computer, scroll through slices, adjust image contrast, zoom into details, take measurements, and inspect the DICOM metadata, all in your browser.

DICOM stands for Digital Imaging and Communications in Medicine. It is the standard used worldwide to store and exchange medical images. A DICOM file can contain pixel data, image dimensions, acquisition details and other information about a medical study.

This viewer is built on Cornerstone3D, the open-source imaging library used by many medical web applications. It saves you installing a desktop program just to look at a scan. Whether a file opens depends on how its image data is encoded, and the viewer tells you plainly when it can’t display one.

What Is a DICOM Viewer?

A DICOM viewer is software that opens and displays medical images stored in the DICOM format. Hospitals and clinics use DICOM for images from CT, MRI, X-ray, ultrasound, mammography and other imaging equipment.

Unlike an ordinary JPEG or PNG, a DICOM file stores medical image pixels alongside structured information: the modality, image size, pixel spacing, and often patient and study details. Some files hold a single image; others hold many frames, such as an ultrasound clip. A CT or MRI study is usually many separate files organised into series.

A viewer reads the image data and presents it in an interface where you can move through slices, adjust window and level, inspect metadata, and measure distances when the file contains calibration information.

How to Use the Free Online DICOM Viewer

Step 1: Select Your DICOM Files

Drag files onto the viewer, or use Browse files, Open folder or Open ZIP. A study copied from a CD or USB drive often sits in a folder with a DICOMDIR index; open the whole folder and the viewer reads the images and skips the index file. Folder selection works in current versions of Chrome, Edge, Firefox and Safari. Want to see how it works first? Use Try a sample scan, a computer-generated phantom with no real patient data.

Step 2: Wait for the Images to Load

The viewer reads each file, checks that it contains DICOM image data in a supported encoding, and groups the images into studies and series. A progress bar shows how far it has got. Large studies and compressed images take longer. Files that can’t be opened are listed with the reason, plus Try again and Remove buttons.

Step 3: Explore the Medical Images

Choose a series in the left-hand list, then use the toolbar, mouse or keyboard:

• Window/level (default): drag to change brightness and contrast. CT images also offer soft tissue, lung, bone and brain presets.
• Pan and Zoom: drag, or use the middle and right mouse buttons. Plus and minus buttons zoom in steps; Fit resets the view.
• Rotate in 90° steps and Invert the greyscale.
• Slices: use the scroll wheel, the slider, the arrow keys, or Play to step through a series or multiframe clip.
• Measure lengths, angles and rectangular regions (area and pixel statistics). Distances are in millimetres when the file includes pixel spacing.
• Full screen and PNG export of the current image.

Step 4: Inspect Available Metadata

Open Image information for key fields such as modality, image size, pixel spacing, window settings and encoding, or All DICOM tags for a searchable list of every tag in the file. Patient identifiers stay hidden until you choose to show them. Missing fields simply aren’t in the file; that isn’t a problem with the image.

Which DICOM Files Can You Open?

Compatibility depends on the file’s encoding (its transfer syntax), not the type of scan. This table shows exactly what we have verified:

CT and MRI Scans

CT and MRI studies usually contain many slices. The viewer groups them into series and sorts them by instance number and position, so scrolling moves through the body in order. Large studies need more time and memory.

X-Ray Images

Digital radiographs are usually single large images. Zoom, pan and window/level let you examine detail; the viewer works with the original pixel values rather than a pre-made picture.

Ultrasound and Other Modalities

Ultrasound often uses multiframe files, which play as a clip. Colour images, such as secondary captures, display in colour. Video-encoded DICOM isn’t supported, and the viewer says so instead of showing an empty screen.

Understanding Window and Level

Medical images often store far more brightness levels than a screen can show. The window is the range of values displayed, and the level (or centre) is the middle of that range. A narrow window increases contrast between similar tissues; a wide one shows more at once. The viewer starts with the values stored in the file, and changing them never alters your original file. The current values are shown in the top-right corner of the image.

What Is the Difference Between DICOM and DCM?

DICOM is the medical imaging standard; .dcm is a common file extension for DICOM data. Many valid DICOM files have no extension at all, especially on CDs from hospitals. Renaming a file doesn’t change its contents, so this viewer checks for the DICOM header inside the file rather than trusting the name.

Are My DICOM Files Uploaded?

No. When you select files, your browser reads them from your device and decodes the images there. The files, image pixels and DICOM metadata are not sent to our server or to any third party. Our automated tests check every network request made while files are opened and confirm that nothing is uploaded.

Loading this page does involve normal network requests: your browser downloads the viewer’s code and image decoders from our server. That’s the same as loading any web page, and it happens whether or not you open a file.

Medical images can contain personal information, so take care on shared or public computers. Use Close all files when you’re finished to clear them from the page’s memory, and close the tab afterwards.

Why Won’t My DICOM File Open?

Unsupported Compression

DICOM allows many compression methods. If a file uses one the viewer can’t decode, it’s listed with the name of the encoding so you can ask the sender for an uncompressed or JPEG copy.

Corrupted or Incomplete Files

A file that was cut short during copying or downloading, or that has no image data (such as a report or DICOMDIR index), can’t be displayed. The viewer tells you which problem it found. Try copying the original file again.

Large Studies

Big studies use a lot of memory. The viewer opens up to 3,000 files or about 1.5 GB at a time. If loading is slow or fails, open one series at a time, close other heavy tabs, or use a device with more memory.

Multiframe or Unusual Image Data

Some files contain many frames or specialised image types. Multiframe images play as a clip. If something displays incorrectly, check the encoding shown in Image information.

Frequently Asked Questions

View Your DICOM Files in Your Browser

Use the viewer to open supported medical images, scroll through slices, adjust the display and inspect metadata, privately on your own device. For anything about what an image means, talk to the doctor or radiologist responsible for the scan.