# Magnification (20x, 40x) and microns per pixel

Source: https://onco.cc/terms/magnification/  
OnCo record `magnification` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Slides are scanned at 20x or 40x objective magnification, about 0.5 or 0.25 microns per pixel; a model trained at one scale can misread tissue at another.

## Summary

Digital pathology scans slides with virtual microscopy at a chosen objective magnification (Wikipedia). 40x resolves nuclear detail at roughly 0.25 microns per pixel and 20x, at roughly 0.5, is the usual compromise between detail and file size; scanners record the exact microns per pixel in the file header. Pathology foundation models are trained at set magnifications and tile sizes, so preprocessing must rescale slides to the training resolution, and a change of scanner is a batch effect for images.

## Fields

- Kind: Term
- Last checked: 2026-09-24
- Also known as: 20x magnification; 40x magnification; microns per pixel; MPP; objective magnification; scan magnification
- Tags: cansim-terms

## Notes

- Listed in the CanSim terms map 1.0.0 (docs/onco/terms.json, generated 2026-09-24), CC BY 4.0, attribution: CanSim project, an open, public-data-first cancer foundation-model programme; CanSim page path /terms/magnification.

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Digital_pathology
- Wikipedia: https://en.wikipedia.org/wiki/Digital_pathology

## Connected records

- terms: [Batch effects and harmonisation](https://onco.cc/terms/batch-effects/), [Cancer AI vocabulary (CanSim terms map)](https://onco.cc/terms/cancer-ai-vocabulary/), [Digital pathology and whole-slide images (WSI)](https://onco.cc/terms/digital-pathology-wsi/), [Tile and patch encoding of slides](https://onco.cc/terms/tile-patch-encoding/)

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JSON: https://onco.cc/api/v1/entities/magnification.json