The number of pills the label counts as one dose — which may be more than one.
Serving size is how many units — capsules, softgels, tablets, or scoops — the supplement-facts panel treats as a single dose. The amounts printed on the panel are per serving, not per pill, so "500 mg" at a serving size of two capsules means 250 mg in each capsule.
Always read the serving size before comparing products: a bottle can look strong or cheap only because its serving is two or three pills instead of one.