How It Works
This calculator works in 4 steps.
Confirm the ppt basis
Select parts per trillion (ng/L), not parts per thousand (g/kg).
Enter the stock
Type the stock in ppm, ppb, or ppt.
Enter the target and volume
Type the ppt target and the final volume.
Read the stock volume and stage plan
The calculator returns V₁ and a multistage plan for factors above 1,000.
The Formula
The formula applies C₁V₁ = C₂V₂ after converting the stock to ppt.
ppt₁ × V₁ = ppt₂ × V₂1 ppt = 1 ng/L = 1 pg/mL1 ppb = 1,000 ppt; 1 ppm = 10⁶ ppt- ppt₁ / ppt₂:
- Stock and target in ppt
- V₁ / V₂:
- Stock and final volumes
To make 100 mL of 100 ppt from a 1 ppb (1,000 ppt) stock, V₁ = 100 × 100 / 1,000 = 10 mL.
Conversion Table
The conversion table shows stock volumes for 5 ultra-trace dilutions.
| Stock | Target | Final volume | Stock volume | DF |
|---|---|---|---|---|
| 1 ppb | 100 ppt (100 ng/L) | 100 mL | 10,000 µL | 10 |
| 10 ppb | 50 ppt (50 ng/L) | 50 mL | 250 µL | 200 |
| 1 ppm | 500 ppt (500 ng/L) | 1,000 mL | 500 µL | 2,000 |
| 100 ppb | 10 ppt (10 ng/L) | 100 mL | 10 µL | 10,000 |
| 1 ppb | 1 ppt (1 ng/L) | 1,000 mL | 1,000 µL | 1,000 |
What Is the PPT Dilution Calculator?
The PPT Dilution Calculator is a tool that dilutes ultra-trace solutions expressed in parts per trillion (ppt) on a stated basis, where 1 ppt equals 1 ng/L in dilute water. Salinity work uses ppt for "parts per thousand", so the calculator asks the user to confirm the trillion basis.
Parts-per-trillion levels apply to per- and polyfluoroalkyl substances (PFAS), dioxins, and some pharmaceuticals in water. The EPA PFAS drinking water rule from 2024 sets a limit of 4 ppt for PFOA and PFOS. The calculator handles conversions from ppm and ppb stocks and recommends 2 or more dilution stages.
Common Uses
There are 5 main uses of this calculator.
PFAS testing
Water labs prepare ng/L calibration standards for EPA Methods 533 and 537.1.
Dioxin analysis
Environmental labs work at pg/L levels with isotope-labeled standards.
Pharmaceutical residues
Researchers measure drugs in surface water at ng/L levels.
Isotope dilution
Analysts prepare ultra-trace isotope spikes.
Method detection limits
Labs prepare low-level spikes to establish detection limits.