Magnification and actual size calculator sim
Drag a clear ruler over seven printed micrographs and drawings to measure the image and the scale bar, then fill a table with the image in mm and µm, the magnification and the real size, with every slip explained.
Cells · covers the O-Level, IGCSE, GCSE topic
What the sim shows
A light microscope on the bench beside a printed card: a micrograph (or a drawing) with its magnification or a scale bar printed under it, and a clear 15 cm ruler lying on top. The close-up shows the card from straight above, with the ruler and the print at one shared scale, so the ruler reads the printed image in true millimetres. Drag the ruler to measure the image, and the scale bar where there is one. Magnification is how many times larger the drawing is than the real thing, so it is the image size divided by the actual size. The two lengths must be in the same unit before you divide, and one is usually in millimetres while the other is in micrometres. There are 1000 micrometres in one millimetre. Magnification has no unit of its own, because it is one length divided by another. Actual size = image size ÷ magnification; image size = actual size × magnification. Units: 1 cm = 10 mm, 1 mm = 1000 µm, 1 µm = 1000 nm. Real sizes used: red blood cell 7.5 µm, cheek cell 55 µm, onion epidermis cell 200 µm long, leaf palisade cell 60 µm long, pollen grain 40 µm, bacterium 2 µm long, mitochondrion 1.5 µm long. Idealised: each print is drawn, not photographed, with its length running left to right; the electron micrographs are black and white, as real ones are.
- The clear ruler: numbered in cm, ticks every mm, its 0 mark 5 mm in from the end
- The close-up: the card seen from above, ruler and print at one scale
- Image size = actual size × magnification, with both lengths in the same unit
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
More biology sims
- Make and stain a temporary slide simDrag onion epidermis or cheek cells onto a slide, add iodine or methylene blue, lower the coverslip at an angle you set with the mounted needle, blot, and see the slide under the microscope: air bubbles, folds or faint cells if a step went wrong, then record and judge each slide.
- Making human insulin by GM simCut the human insulin gene and a plasmid with the same restriction enzyme, see the sticky ends pair base by base, seal them with DNA ligase, put the plasmid into bacteria, select them on antibiotic agar and grow them, one step at a time and in order.
- Monohybrid cross simChoose the parent pea plants, drag their gametes and the genotypes into a Punnett square, then breed 4, 40 or 400 offspring and compare what you get with the expected ratio.
- Plant tropisms and auxin simGrow a bean seedling with light from one side, on its side in the dark or turning on a clinostat, wait a day at a time, measure each tip's angle with a protractor, graph your readings and see where the auxin goes in the shoot and the root.
- Quadrats and transects simPlace a quadrat at random coordinates on a model field, count the daisies with the edge rule, work out the mean, density and estimated total from your own counts, then run a transect from a tree's shade into the open, reading a light meter and counting grass cover in a gridded quadrat.
- Reaction time (ruler drop) simLine up a 50 cm rule with the catcher's thumb, drop it, read the catch on a magnified scale, convert it to a reaction time, take ten repeats and a mean, spot the anomaly, and compare practice, distraction, caffeine and alcohol on a bar chart of your own means.