How to Check Image Size, Aspect Ratio and DPI (5 Easy Ways)

Published 1 November 2026 · By Sardar Zain, Founder of Orixiva · 11-minute read

“Image must be 1080 × 1350.” “Upload at 300 DPI.” “Use a 16:9 thumbnail.” Before you can fix an image, you need to know what you have. This guide shows you how to check image size in pixels, find the aspect ratio, read the DPI, and work out how big you can print, on any phone or computer.

You will also learn what these numbers really mean (DPI is the most misunderstood of all) and how to check everything at once with the free Orixiva image dimension analyzer, which runs in your browser without uploading your files.

Image size, aspect ratio and DPI: what they mean

When a website says “maximum image size 2MB”, it means file size. When it says “image size 1200 × 628”, it means dimensions. Knowing which one you are dealing with saves a lot of failed uploads.

How to check image size online (step by step)

This is the fastest way to see every number at once, for one image or hundreds.

1. Open the analyzer. Go to the free image dimension analyzer. It accepts JPG, PNG, WebP, GIF, AVIF, SVG, BMP, TIFF and HEIC.
2. Add your images. Drop files or a folder, click Choose images, paste with Ctrl+V, or paste an image address into Image URL and press Analyze URL. Nothing is uploaded.
3. Read the Overview. Dimensions & ratio shows width, height, megapixels and the aspect ratio. Resolution & print size shows the DPI and how big it prints. File & encoding shows the format and file size.
4. Measure inside the image (optional). Open Measure and use the 📏 ruler or ▭ box to measure any part in px, %, inches, cm or mm. The 💧 tool reads colours.
5. Test it against a platform. Open Size check to see if the image fits common sizes, with a crop preview.
6. Get resize numbers and code. Resize & code has an aspect ratio calculator, a print calculator, and ready HTML and CSS.
7. Save or share the result. Press Copy summary, or Download report (JSON). For many files, All images exports a CSV.

How to check image dimensions on Windows, Mac, iPhone and Android

Built-in options show the pixels, but rarely the ratio or print size. Here is where to look:

How to find the aspect ratio of an image

Divide the width and height by their greatest common divisor (the biggest number that divides both). For 1920 × 1080, that number is 120, so 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9: the aspect ratio is 16:9.

How to resize without changing the aspect ratio

Keep the ratio and change one side: new height = new width × (old height ÷ old width). A 4032 × 3024 photo at 1200 px wide becomes 1200 × 900. The analyzer’s Aspect ratio calculator does this as you type: change the width, height or scale, and the other values follow.

How to check image DPI (and why it rarely matters)

DPI (dots per inch) and PPI (pixels per inch) are often used as the same thing. In a digital file, it is just a number stored in the metadata, such as 72 or 300. It tells a printer how many pixels to place in each inch of paper.

Here is the key point: changing the DPI number does not change the pixels. A 1200 × 800 image looks exactly the same on screen at 72 DPI or 300 DPI. Only the printed size changes: 16.7 × 11.1 inches at 72 DPI, or 4 × 2.7 inches at 300 DPI.

• For websites, social media and email: ignore DPI. Only pixel dimensions and file size matter.
• For printing: check that you have enough pixels for the print size at the DPI you need.
• When a form demands “300 DPI”: it usually means “enough pixels to print sharply”. Check the print size at 300 DPI in the analyzer.

To check image DPI, open Resolution & print size in the analyzer. On Windows, Properties → Details also shows “Horizontal resolution” and “Vertical resolution”.

How big can you print a photo?

Print size in inches = pixels ÷ DPI. Pixels needed = inches × DPI. At 300 DPI (photo and magazine quality):

In the analyzer, Pixels needed for print works this out for you: type a print size in inches, cm or mm, choose 150, 240, 300 or 600 DPI, and it tells you if your image is big enough.

Will your image fit? Common platform sizes

Most failed uploads are a wrong shape, not a wrong size. These are widely used recommended sizes; platforms change their guidelines, so always check the latest help page before a big campaign. For example, YouTube’s thumbnail help page now asks for thumbnails “as large as possible” (it suggests 3840 × 2160 for videos) with a minimum width of 640 pixels; 1280 × 720 remains a safe, widely used size.

The analyzer’s Size check tab compares your image with sizes like these and shows two options: Fill (crop), where the edges are cut, and Fit (add bars), where the whole image shows with bars. Select a row to see the crop preview, or enter a custom width and height.

Image dimensions for websites (and the code to use)

On a website, an image should be about as wide as the space it fills, and no more. A 4000 px photo in a 800 px column wastes data and slows the page. Two habits help:

• Always set width and height in the HTML. It lets the browser reserve the space and prevents content jumping while the page loads (layout shift, measured as CLS). The analyzer’s HTML & CSS for this image writes the correct tag for you.
• Serve several sizes with srcset. The analyzer suggests a responsive srcset up to the original width. To create those files, use the bulk image resizer, which makes every size at once.

More image speed tips are in our on-page SEO checklist. If a file is still too heavy after resizing, the free image compressor can bring it under a target like 100KB.

Megapixels: how many do you really need?

Megapixels (MP) are width × height ÷ 1,000,000. More is not always better: it means larger files and slower pages. What you need depends on the job:

So a normal 12 MP phone photo is already enough for an A4 print. For screens, it is far more than needed, which is why resizing before upload matters.

Example: one photo, three destinations

You have a 4032 × 3024 (4:3) photo from a trip and want to print it at 8 × 10 inches, post it on Instagram and use it on your website. Here is how to check image size and plan each version:

1. Print: 8 × 10 in at 300 DPI needs 2400 × 3000 px, a 4:5 shape. The photo has enough pixels, but it is 4:3, so you must crop. Pixels needed for print confirms it is big enough.
2. Instagram: the portrait post is also 4:5 (1080 × 1350). Use Size check, choose Fill (crop) and look at the crop preview to make sure no heads are cut.
3. Website: the content column is 1200 px wide. The aspect ratio calculator gives 1200 × 900 at the original 4:3 shape, and the HTML tab gives the image tag with width and height.

Three checks, one tool, and no guessing. Then create the files with the bulk resizer or an editor.

Why does my image look blurry after uploading?

When an upload looks soft or blocky, the image dimensions are usually the cause, not the camera. Common reasons:

• Too small for the space: a 600 px image stretched across a 1,200 px banner is enlarged by the browser and looks blurry. Check image size against the space it fills.
• Wrong shape: the platform crops and rescales an image whose aspect ratio does not match, often losing sharpness.
• Re-compressed by the platform: social networks compress big uploads again. Uploading at the recommended size gives them less reason to.
• High-density screens: phones and retina laptops show 2–3 device pixels per CSS pixel, so a 400 px wide slot looks best with an 800 px or larger image.

The analyzer’s Screen & colour section and Size check tab help you spot these problems before you upload.

Checking many images at once

Auditing a product folder or a website’s uploads? Drop the whole folder. The All images tab lists every file with its dimensions and ratio. Filter by orientation (landscape, portrait, square), show only images narrower than a width you set (handy for finding images too small for a theme), and see which images share the same dimensions. Export the table as CSV or JSON for a spreadsheet.

The analyzer also shows camera details and metadata. If a photo contains GPS location, the Open in EXIF remover link takes you straight to the EXIF remover to clean it.