How many units belong in a forehead depends on who you ask, and the published figures form a range rather than one number. This page lays out the counts Healthline reports and the questions to settle before any of them is applied to you.
The unit counts Healthline reports
Healthline says some practitioners inject an average of 10 to 30 units into the forehead. It adds that the manufacturer of Botox Cosmetic suggests a dosage of 4 units in each of five sites on the forehead, totaling 20 units.
For horizontal forehead lines, Healthline says practitioners can inject up to 15 to 30 units of the toxin. For the "11" lines between the eyes, it says up to 40 units are indicated, with higher doses needed in male patients.
The American Society of Plastic Surgeons keeps a botulinum toxin page on the cosmetic procedure if you want a second source.
Reading a range
Treat these counts as published reference points. They do not prescribe a dose for your face, and the number that applies to you is a decision for the clinician who examines you.
Cleveland Clinic explains what Botox is, its results and side effects if you want background on the treatment before the appointment.
Questions that can wait for the consultation
Dose is a planning question, so it can wait until you sit down with your injector. Ask how many units they plan for each area and why that count suits you. Cleveland Clinic's page on cosmetic injectables is the clinic's own overview of the service.
After the injection
If something looks or feels wrong after treatment, that is a separate question from dose, and the clinician who treated you is the right person to ask. Cleveland Clinic's Botox Cosmetic page on uses and side effects covers side effects in more detail.