image tool
Check image size online
Drop up to 20 images to check their size online: width and height in pixels, aspect ratio, megapixels, file size, format and colour depth, read straight from each file's header. Each image is also checked against a 300 KB web page budget and the 8 flyer canvas sizes.
Loading the tool…
- Runs on your device, nothing is uploaded
- Free, no sign in
- No watermark, no file limit
How it works
- 1
Choose the images
Click Choose up to 20 images, or drop them on the box. Only the start of each file is read.
- 2
Read each card
Every image gets a card with its dimensions, aspect ratio, megapixels, file size, format and colour depth, plus a 300 KB verdict.
- 3
Check the flyer sizes
Open Fills N of the 8 flyer canvases to see, for each size, whether the image covers it sharp or would be enlarged, and how much a centre crop cuts off.
- 4
Export or check more
Copy the results as CSV, download them, or press Check other images to start a new batch.
Header only, so it is fast
Every image format stores its pixel size near the start of the file: a PNG in its first chunk, a JPEG in its frame marker, a WebP in its first block, an AVIF or HEIC in an image size box. This checker reads those bytes and stops, so a 40 MB camera file is measured as quickly as a small icon and nothing is decoded. A file with a damaged header shows as unknown rather than as wrong numbers; damage further into the picture is not seen.
The numbers that matter
Width and height decide how large an image can be shown before it looks soft. Aspect ratio decides how it crops: a 3:2 camera photo placed in a square loses a third of its width. File size decides how fast a page loads. Colour depth tells you whether the file has an alpha channel for transparency, and whether a JPEG is in CMYK, which some web browsers and apps show with odd colours.
The 300 KB budget
300 KB is a common ceiling for a single image on a web page, and it is the limit this site holds its own images to. Most photos for the web can meet it at 1200 to 1600 pixels wide as a WebP or a well compressed JPEG. A card over budget says by how much, so you know whether a light compression will do or the image needs resizing first.
Will it fill a flyer?
The flyer builder has 8 canvas sizes: A4 portrait and landscape at 1240 by 1754 pixels, Instagram post at 1080 square, Instagram story at 1080 by 1920, Facebook post 1200 by 630, LinkedIn post 1200 by 627, Facebook cover 820 by 312 and Twitter header 1500 by 500. For each, the checker works out the scale needed to cover the whole canvas. Sharp means no enlarging is needed; otherwise it says by how much. Uploaded flyer images are centre cropped to fill their slot, so the crop figure shows how much of the picture would be lost.
Limits worth knowing
Only the header is read, so a file with a corrupt or cut short header shows as unknown with the reason, and damage past the header goes unnoticed. AVIF and HEIC report the stored size before any rotation, and SVG reports a nominal size because a vector has no pixels. Nothing leaves this page: each file is read in your browser, nothing is uploaded and nothing is stored, ever.
Limits
- Reads the header only, so a file whose header is corrupt or cut short shows as unknown, with the reason. Damage further into the picture is not detected.
- AVIF and HEIC sizes are as stored, before any rotation the file asks for.
- SVG has no fixed pixel size; the size shown is the nominal one from its width, height or viewBox.
What it does not do
- It does not resize or compress. The image resizer and the image compressor do.
- It does not read DPI or print size. The DPI calculator works those out.
- It does not show EXIF details such as the camera or the date taken.
Questions people ask
How do I find an image's size on a phone?
On iPhone, open the photo in Photos and swipe up, and the size appears under the date. On Android, Google Photos shows it under the details menu. Both show pixels and file size but not colour depth or aspect ratio. This page works in a phone browser too, and checks up to 20 photos in one go.
Why does the file size not match the pixel size?
Compression. A 4000 by 3000 photo holds 12 million pixels, which is 36 MB uncompressed, but a JPEG might store it in 3 MB and a WebP in 2 MB. Flat graphics compress far better than detailed photos. Two images with identical dimensions can therefore differ tenfold in file size, which is why both numbers are shown.
What does colour depth tell me?
How many bits describe each pixel. 8 bit RGB is the normal 24 bits per pixel for photos; 8 bit RGBA adds an alpha channel for transparency; a palette PNG holds at most 256 colours and suits logos and icons. A 16 bit PNG holds finer gradations for editing, but most screens show 8 bits, so it mostly adds size.
Why does a HEIC photo show a sideways size?
Phones store the picture as the sensor captured it and add an instruction to rotate it on display. The checker reads the stored size from the header, before that instruction, so a portrait photo can be reported as landscape. Once the photo is opened and saved as JPEG or PNG, the rotation is applied and the size reads the right way round.
Is a bigger image always better for a flyer?
Only up to a point. An image that covers the canvas without enlarging prints sharp; going beyond twice that size adds file weight without adding visible detail. The flyer builder exports images at twice the canvas size, so an A4 portrait photo of about 2480 by 3508 pixels is as sharp as the export can show.
Put the photo on a flyer that fits it
Take what you made here into flyers.
Create a flyer with OneCraftMore tools like this
- Image resizerResize a batch of images to an exact width, height or percentage. Fit, fill or stretch, with a stepped downscale that keeps detail. Nothing is uploaded.
- Image compressorCompress to WebP or JPEG and compare the result against the original under a divider you drag. Or ask for a size in KB. Nothing is uploaded.
- Flyer size resizerDrop a flyer and see it refitted onto all ten builder canvases at once, each drawn at its true shape, with the ones that will print soft flagged in words.
- DPI calculatorEnter a pixel size and a print size and see the sheet drawn at real proportions, the area your file covers sharply, and a plain verdict on whether it will do.
- Aspect ratio calculatorType a size and see your shape drawn against any target: the bars if you fit it whole, the crop if you fill it. Presets for print, screen and social.
Background reading: the question page on this.
Written and checked by the OneCraft team. Last checked .