Which Bac Water Size Should You Buy: 3, 5, 10 or 30 mL?
By the BacWater.fit team · Updated
Short answer. Buy the vial you will finish within 28 days of first puncturing it. Light use (a few mL a month) suits 3 or 5 mL; up to about 10 mL in 28 days suits 10 mL; around 30 mL in 28 days suits 30 mL. Whatever is left on day 28 is thrown away, so a bigger vial only saves money if you use it up.
| 3 mL · kit of 10 | $13.00 a kit · 30 mL of water · $0.43 per mL |
|---|---|
| 5 mL · kit of 10 | $14.00 a kit · 50 mL of water · $0.28 per mL |
| 10 mL · kit of 10 | $15.00 a kit · 100 mL of water · $0.15 per mL |
| 30 mL · kit of 25 | $155.00 a kit · 750 mL of water · $0.21 per mL |
The 28-day window decides it
An opened multi-dose vial is normally dated when it is first punctured and discarded 28 days later unless its label says otherwise. Size the vial to what you draw in that window, not to what looks cheapest on the shelf.
Price per millilitre is not the whole story
The table above shows what a millilitre costs in each kit. Water you discard on day 28 still counts: a 30 mL vial used for 6 mL costs five times its per-mL price for the water you actually used.
When the small sizes win
- You reconstitute rarely, or only one vial at a time.
- Several people would otherwise share one opened vial.
- You want a fresh, unopened vial each time and spares that keep until their expiry.
Let the Size Finder do the arithmetic
Enter how many millilitres you draw per week or month and the period you want to cover. The Size Finder returns the size that wastes least and the number of kits, with the kit price.