Measure before ordering
Head circumference is taken with a tape measure, horizontally, passing above the eyebrows at the front and over the bump of the inion at the back. It is the same circumference used to compute the 10-20 positions, which is no coincidence.
A department seeing general adults covers the great majority of its patients with three sizes: 50-54, 54-58 and 58-62 cm. A paediatric department needs the lower range, and neonatology goes below 34 cm, where you move to the Multicap Cup.
Between two sizes, take the smaller. A slightly stretched cap presses the electrodes down; a cap that is too wide lets them float, and no amount of gel makes up for a contact that does not press.
| Head circumference | Population | Electrodes | Head circumference |
|---|---|---|---|
| 34 à 38 cm Brown | Child | 10 | |
| 38 à 42 cm Pink | Child | 10 | |
| 42 à 46 cm Light blue | Child | 20 | |
| 46 à 50 cm Green | Adult | 20 | |
| 50 à 54 cm Yellow | Adult | 20 | |
| 54 à 58 cm Red | Adult | 20 | |
| 58 à 62 cm Blue | Adult | 20 |
Measure head circumference above the eyebrows and the inion before ordering. A size too large does not press the electrodes down, a size too small leaves a mark by morning.
How many caps you actually need
A reusable cap has to be washed and dried flat between two patients. Drying takes several hours, and that is what sizes the stock, not the number of studies.
For a lab running two patients a day on the same size, at least three caps of that size are needed: one on the patient, one drying, one ready. With only two, the third day runs on a cap that is still damp, and damp makes bridges between electrodes.
That is where disposable changes the calculation. A Dispocap or a Netcap removes the drying, so it removes the buffer stock. On irregular activity or in isolation, it often works out cheaper than reusable once the cleaning time is counted.