Scale Bar Measurement Tool

Measures lengths, areas, angles and particle sizes on SEM and microscope images, using the scale bar in the image as the reference. Use it to take dimensions from an image without installing ImageJ.

How to use

1. Drop the image on the page, or click to choose it. PNG, JPG, WebP and 8/16-bit TIFF open.
2. With "Set scale", click both ends of the scale bar and enter the "Real length of the scale bar" and unit. If you know the length of 1 px, choose "Type it in".
3. Pick a tool such as "Distance", "Angle", "Circle" or "Polygon" and click on the image. Drag points with "Select / move" to correct them.
4. Check "Measurements" and "Statistics", then export with "Save as CSV", "Copy table" or "Save PNG with dimensions".

How it works

• Real length = pixel length × (scale bar length ÷ scale bar pixels); areas use the square of this ratio. Without a scale, values are in px.
• Two or more measurements of one kind give the count, mean, standard deviation, minimum and maximum. A TIFF calibrated in ImageJ can use its own scale.
• Accuracy depends on how precisely you click the scale bar ends. Perspective from tilted samples is not corrected.
• The image is processed in your browser and not sent anywhere. Work on each image is saved on this device.

Questions and answers

How do I measure particle size on an SEM image?

Set the scale first, then draw a "Distance" line across each particle or outline it with "Circle". "Statistics" shows the mean and standard deviation.

Can I measure an image without a scale bar?

Enter the length of 1 px with "Type it in", or click a printed map scale or a ruler in the photo as if it were a scale bar.

Can it open TIFF files?

Uncompressed, LZW and Deflate TIFF in 8, 16 or 32-bit greyscale or 8 or 16-bit colour. Save other kinds as PNG first.

Is it suitable for unpublished research images?

The image is not sent to a server; it is processed only inside this browser.