Online Scale Bar Maker for SEM, TEM & Microscopy Images

Intermediate

How to Add a Scale Bar to an SEM Image Online Without ImageJ

In this guide, you will learn a simple and fast workflow for creating accurate SEM scale bars without complicated image processing steps.

Mohammad Ali ZandiSeptember 18, 2026Updated: October 12, 20263 min

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What You Need Before You Start

A SEM image available in the Image Library.
A known reference length for manual calibration.
Login is required to export the image.

Step 1: Open NotyScale and Load Your SEM Image

Before calibration and adding a scale bar, keep this in mind:

If the scale reference is separate from the image: Do not resize the image before calibration. Resizing changes the pixel-to-length relationship.
If the original scale bar is already visible on the image: Resizing is fine, as long as the image and scale bar are resized together without changing the aspect ratio.

If your image has not been calibrated in NotyLab before, switch to Workflow at the top.

Workflow guides you through calibration and scale bar creation step by step, without switching between different tools.

Start Workflow Free

Open the Image Library, choose an image from the embedded picker, and select it to load it into NotyScale.

Step 2: Calibrate the SEM Image

Select Manual Calibration to begin drawing a two-point reference line on the image canvas.

Draw a Reference Line

On the canvas, set the two endpoints of the reference line. Use the canvas controls as needed to view the reference clearly, then select Continue.

Enter the Known Length and Unit

Enter the known reference length and select the unit that matches your SEM image, such as nm or µm. In this example, the reference is entered in µm.

Select the workflow control to continue to the next available step.

Step 3: Prepare or Crop the Image (Optional)

Open Image Preparation from the Image setup card. On the preparation canvas, define a crop, add it to the draft, and apply the draft to create the effective image.

Step 4: Add and Customize the Scale Bar

Choose the Publication Preset

In Auto Create, select Publication, then select Add Scale Bar.

Set the scale-bar length

Open the Layout tab and change the Length value in the current display unit.

Step 5: Export the SEM Image

Select Export Image to open the export dialog for format and resolution selection.

Return to the NotyScale workspace page after configuring the scale bar and export options.

Your SEM image is calibrated and now contains an accurately sized scale bar ready for export.

Common SEM Scale Bar Mistakes

Adding scale bar before resizing
Using incorrect calibration
Exporting low-resolution figures
Using unreadable labels
Stretching the image

Notes

Use a reference line with a known real-world length when manually calibrating.
Applying Image Preparation commits draft crop or erase actions as the new effective image.

Frequently Asked Questions

Can I add an accurate scale bar to an SEM image without ImageJ?

Yes. You can use NotyScale to calibrate the SEM image from a known reference distance and then add a scale bar with the correct real-world length and unit.

What do I need to calibrate an SEM image?

You need reliable scale information, such as an existing scale bar, a known reference distance, or valid spatial calibration information from the microscope. Without a known relationship between pixels and real-world distance, an accurate scale bar cannot be created.

Can I use the existing scale bar in my SEM image for calibration?

Yes. If the original SEM image already contains a scale bar, you can draw the calibration reference along that bar and enter its known length and unit.

Should I remove the old scale bar before calibrating the image?

No. If the old scale bar is your calibration reference, calibrate the image first. After the calibration is saved, you can crop or remove the old bar and add a new publication-ready scale bar.

Does resizing an SEM image affect scale-bar accuracy?

It can. Resizing the image before calibration changes the relationship between pixels and real-world distance. If an image and its existing scale bar are resized together proportionally, their geometric relationship is preserved. Avoid stretching the image or resizing the image independently from its scale bar.

Can I use nm instead of µm for an SEM scale bar?

Yes. The unit should match the scale of your image and the calibration information you have. SEM images may use nm, µm, or other appropriate length units depending on the field of view.

What scale-bar length should I use for an SEM image?

There is no single correct length for every SEM image. Choose a simple, readable value such as 1, 2, 5, 10, 20, or 50 in the appropriate unit, depending on the field of view. The bar should provide useful scale information without covering important image features.

Can I create an accurate scale bar using only the SEM magnification value?

Magnification alone is usually not the best basis for calibrating an exported digital image. For reliable results, use the image's spatial calibration, a known reference distance, or an existing scale bar.

Can I crop my SEM image after calibration?

Yes. Cropping does not normally change the pixel-to-distance relationship as long as the image is not rescaled. In NotyScale, you can calibrate the image first, prepare or crop it, and then add the final scale bar.

What should I check before exporting an SEM image for publication?

Check that the calibration and unit are correct, the scale-bar length is appropriate, the label is readable, the bar does not cover important features, and the image has not been stretched. Also export at a resolution suitable for your intended publication.