How do I calculate pixel size from a scale bar?

Measure the scale bar length in pixels using ImageJ/FIJI. Divide the labeled scale bar value by the measured pixel count. Example: 500 nm scale bar measuring 200 pixels = 2.5 nm/pixel.

What is the relationship between magnification and pixel size?

Pixel size = Detector pixel size / Magnification. For 14 µm detector at 50,000×: 14,000 nm / 50,000 = 0.28 nm/pixel.

TEM/SEM Scale Bar & Magnification Calculator

Verify pixel-to-nanometer ratios, calculate field-of-view, and validate scale bar accuracy in electron micrographs

Scale Bar Measurement

Auto-Update

Scale Bar Length (as labeled)

Enter the value printed on the scale bar

Scale bar length must be greater than zero

Scale Bar Pixel Length Measured in ImageJ/FIJI

pixels

Include uncertainty ±

Pixel count must be greater than zero

Image Dimensions Optional

× px

Lock ratio

Aspect ratio: 1:1 (square)

Results

Pixel Size

— nm/pixel

Field of View (Width)

— µm

Field of View (Height)

— µm

Pixels per nm

— px/nm

Est. Magnification

— ×

Detector & Magnification

Auto-Update

Detector Pixel Size

Detector pixel size must be greater than zero

Total Magnification

Include uncertainty ± %

Magnification must be greater than zero

Binning Factor

Image Dimensions Optional

× px

Results

Calculated Pixel Size

— nm/pixel

FOV Width

— µm

FOV Height

— µm

Effective Detector Pixel

— µm

Nyquist Limit

— nm

Enter values to calculate

Scale Bar Validation

Auto-Update

Measured Pixel Size (from scale bar)

Value must be greater than zero

Expected Pixel Size (from magnification)

Value must be greater than zero

Tolerance

Results

Discrepancy

— %

Calibration Status —

Enter both values to validate

Absolute Difference

— nm/px

Correction Factor

— ×

Multiplies your measured scale bar length by 1.0000 to match expected calibration

Understanding Scale Bars in Electron Microscopy

Scale bars establish the relationship between pixels and physical dimensions. The pixel size depends on magnification, detector pixel size, and digital processing.

Key Equations

From Scale Bar: Pixel Size = Scale Bar Length ÷ Scale Bar Pixels

From Magnification: Pixel Size = Detector Pixel Size ÷ Magnification

Field of View: FOV = Pixel Size × Number of Pixels

Nyquist Limit: Minimum resolvable feature = 2 × Pixel Size

Common error: Digital zoom or cropping changes effective magnification but may not update the scale bar.

Calibration Standards

Standard	Feature Size	Magnification
Cross-grating	463 nm	1k–50k×
Latex spheres	100–1000 nm	10k–100k×
Gold nanoparticles	5–50 nm	50k–500k×
Gold lattice (111)	0.235 nm	>200k×

References

Williams, D.B. & Carter, C.B. (2009). Transmission Electron Microscopy. Springer.

ISO 16700:2016. SEM magnification calibration guidelines.

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TEM/SEM Scale Bar & Magnification Calculator

Scale Bar Measurement

Results

Detector & Magnification

Results

Scale Bar Validation

Results

Understanding Scale Bars in Electron Microscopy

Key Equations

Calibration Standards

References

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