Biology · Grades 7–11
Actual size from an image
Magnification is image size divided by actual size. Convert millimetres to micrometres consistently.
Rule and assumptions
Magnification is image size divided by actual size. Convert millimetres to micrometres consistently.
actual size (µm) = image size (mm) × 1000 / magnification
Worked examples
A printed image is 26 mm long at 400× magnification. Find the actual length in micrometers. Round to 3 decimal places if needed. Answer in µm.
actual size (µm) = image size (mm) × 1000 / magnification 26 × 1000/400 = 65
65 µm
A printed image is 58 mm long at 50× magnification. Find the actual length in micrometers. Round to 3 decimal places if needed. Answer in µm.
actual size (µm) = image size (mm) × 1000 / magnification 58 × 1000/50 = 1160
1160 µm
Try two questions
A printed image is 77 mm long at 40× magnification. Find the actual length in micrometers. Round to 3 decimal places if needed. Answer in µm.
A printed image is 15 mm long at 100× magnification. Find the actual length in micrometers. Round to 3 decimal places if needed. Answer in µm.
Answers and reasoning
Answers and marking notes
- 1925 µm
actual size (µm) = image size (mm) × 1000 / magnification 77 × 1000/40 = 1925
- 150 µm
actual size (µm) = image size (mm) × 1000 / magnification 15 × 1000/100 = 150
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.