How to measure a spore

What you need

You need a microscope, a graticule in one eyepiece and a stage micrometre. The equipment page lists them.

Step 1: calibrate the graticule

Nikon describes the method in five moves.

1. Bring the graticule and the stage micrometre into focus together.
2. Line the two scales up in parallel.
3. Find two points where the lines match exactly.
4. Divide the known length between those points by the number of graticule divisions between them.
5. The answer is the micrometres in one graticule division.

Use as many stage graduations as you can. Nikon says it is never advisable to rely on one ten-micrometre division alone. Repeat the calibration for each objective.

Step 2: measure each spore

Length is the longest dimension of the spore. Width is measured across the widest point, at right angles to the length. Count graticule divisions for each. Multiply by the calibration value.

Let the spores settle before you measure them. Measure at the same magnification you used to calibrate.

Step 3: decide how many spores to measure

The sources found here set no fixed number. Published studies vary widely. One study measured 920 to 2322 spores per species across 23 to 47 specimens.

Choose a number before you start. Write it down and report it. More spores give a steadier mean.

Step 4: record and report a range

Report a range, not one figure. Use this pattern:

• length range x width range, in micrometres
• mean length x mean width
• Q (length divided by width), as a range and a mean
• N, the number of spores measured
• magnification, mounting liquid, date and calibration value

A published study recorded measurements to the nearest micrometre and gave N for each specimen. Drying changed length and width in that study, so state how the sample was mounted.

Why readings differ

Two people can measure the same sample and get different numbers. These are the usual reasons.

• Spore age. Scottish Fungi says size and ornamentation can vary between immature and mature spores.
• Mounting. Drying and the mounting liquid changed length and width in a published study.
• Objective. Each objective has its own calibration value. Never mix them.
• One division. Nikon says never to rely on a single ten-micrometre division.

Write each of these on the record sheet, so a later reading can be compared fairly.

Worked example

Example only: not a measurement of our syringes. Every number below is invented.

Calibration. Seven divisions of the stage micrometre, 70 micrometres, match 56 graticule divisions. So one graticule division is 70 divided by 56, or 1.25 micrometres.

The mean length is 11.0 µm and the mean width is 6.75 µm. The mean Q is 1.63.

Reported to the nearest micrometre, the invented sample reads as follows.

• Length x width: 10-13 x 6-8 µm
• Mean length x mean width: 11 x 7 µm
• Q: 1.5-1.8, mean 1.6
• N = 10, 1000x, water mount, calibrated on the day

One graticule division is 1.25 µm here, so no single reading is finer than that. Ten spores is too few for a real report. It keeps the table short.

Published ranges

Published descriptions of Psilocybe cubensis give spore size as a range, and the ranges are not identical across papers. Check any figure against the paper it came from. Across Singer and Smith (1958) and Batista et al. (2025), published figures run from about 11.5 to 17 by 6 to 11.5 µm.