The Ordinary sells most of its serums in 30 ml bottles, which hold roughly 600 drops at about 0.05 ml each. At the recommended 2-3 drops per application, once daily, a single bottle gives you 200-300 uses - meaning most people get 3 to 5 months of consistent use before running out.
How many applications are in a 30 ml The Ordinary bottle?
One drop is about 0.05 ml, so a 30 ml bottle contains roughly 600 drops. The Ordinary and most dermatologists recommend 2-3 drops per application for a full face. At 2 drops that's 300 applications; at 3 drops it's 200. If you apply morning and night, a bottle can disappear in 7 to 10 weeks.
The Ordinary also sells some formulas in 60 ml sizes (about 1,200 drops), which doubles the runway to 14-20 weeks at the same frequency. Check the size before ordering - the price difference is rarely exactly double, so the per-ml cost changes.
Cost per use on popular The Ordinary formulas
The Ordinary's prices are notably low compared with most serums. A 30 ml bottle of Niacinamide 10% + Zinc 1% typically runs around $6-7, which works out to roughly 2-4 cents per application at 2-3 drops. The AHA 30% + BHA 2% Peeling Solution (30 ml, around $8-9) is used weekly rather than daily, so a bottle can last 6 months or longer even though the bottle is the same size.
The Buffet (30 ml, typically $14-16) and Hyaluronic Acid 2% + B5 (30 ml, around $10-12) cost more per bottle but still land under $0.10 per use daily. That makes them genuinely cheap on a per-use basis compared with most mid-range serums priced at $40-60 for the same volume.
To get your own number, plug the exact price and how many drops you use into the longevity calculator above. It will also tell you if the PAO expiry (usually 12M for The Ordinary serums) will beat the bottle before you finish it.
Does the PAO matter for The Ordinary serums?
Most The Ordinary serums carry a 12M PAO (12 months after opening). At daily use that rarely matters - you'll finish a 30 ml bottle in 3-5 months. Where it does bite you is with occasional-use products like the AHA/BHA exfoliant or Glycolic Acid 7% Toning Solution. Use those once or twice a week, and the 12M clock is the binding constraint, not the bottle level.
If you are approaching the 12-month mark on an open bottle, check whether the color, consistency, or scent has changed. Active ingredients like vitamin C (Ascorbyl Glucoside Solution 12% or the pure L-Ascorbic Acid Powder) degrade faster than most. The PAO is a minimum guideline, not a hard expiry, but it is the point at which the brand no longer guarantees potency.
Tips to make The Ordinary bottles last longer
Press-and-hold the dropper rather than squeezing and releasing repeatedly - you draw less product per drop and waste less in the pipette. A pea-sized amount (about 0.2 ml, or 4 drops) is the upper end of what absorbs fully on most skin types; using more does not increase efficacy.
Store bottles away from heat and direct light. The Ordinary's formulas are sensitive to oxidation, and a dark, cool shelf extends both the effective life and the PAO-limited window you are paying for.