PPM Calculator
Work out parts per million from a solute and a total, or find the dose needed for a target ppm.
Solute needed at 250 ppm
| Batch size | Solute | Equivalent |
|---|---|---|
| 1 L | 250 mg | 0.26 US gal |
| 5 L | 1.25 g | 1.32 US gal |
| 10 L | 2.5 g | 2.64 US gal |
| 20 L | 5 g | 5.28 US gal |
| 100 L | 25 g | 26.42 US gal |
| 1,000 L | 250 g | 264.17 US gal |
What ppm means
One part per million is one unit of solute in a million units of mixture:
ppm = (solute ÷ total) × 1,000,000
Because it is a ratio, both quantities must be in the same kind of unit. 5 g in
20 kg is 5 ÷ 20,000 × 10⁶ = 250 ppm.
The useful shortcut for water
One litre of water weighs one kilogram, so 1 ppm is 1 mg per litre — and 1 g in 1,000 L. That makes dosing arithmetic easy: to hit 250 ppm in 20 L you need 250 × 20 = 5,000 mg, or 5 g.
This calculator treats litres and gallons as water for that reason. For a denser liquid, work in mass or use the ppm to mg/L converter with the real density.
Solute in the total, or added to it?
Strictly, ppm is solute divided by the total mixture including the solute. In dilute solutions the difference is negligible — at 250 ppm it changes the answer by 0.025% — but at high concentrations it matters. At 100,000 ppm (10%), treating 100 g added to 1 kg of water as 100,000 ppm rather than the correct 90,909 ppm is a 10% error.