dropper-bottle dropper volume:

How do you get a whole dropper full of the tincture into the glass dropper? When you squeeze the bulb only 1/3 of the dropper gets filled! 1/3 of the dropper is actually one dropper full, or the amount you can get into the dropper with one squeeze. We know it can be a little confusing when you’re new to using tinctures! So! Zoi friends, remember that 1 dropper full = 1/3 of the glass dropper, which = 0.5 ml. A typical adult dosage is 1.5 ml or about 3 droppers full.

My actual own measurement (using a 30-ml dropper bottle):

1 bulb squeeze gets 0.5-0.6 ml or half the dropper length. dropper has volume notches. full dropper is 1 ml.

0.5 ml yields 17 drops.