By Athena Hessong
Updated Mar 24, 2022

Ryan McVay/Photodisc/Getty Images

In scientific measurements, the concentration of trace components in a solution is frequently expressed in parts per million (ppm). This unit can refer to anything from gases and metals to sediments and contaminants in a liquid or gaseous mixture. When a finer resolution is needed, especially in environmental monitoring, the same concentration may be expressed in parts per thousand (ppt).

Step 1 – Understand the Conversion Formula

The relationship between ppm and ppt is straightforward: 1 ppm = 0.001 ppt. Therefore, to convert a value from ppm to ppt, simply divide by 1,000.

Step 2 – Apply the Formula

Take the ppm measurement and divide by 1,000. For example, if you measure 340,000 ppm of carbon dioxide in the atmosphere, the calculation is:

340,000 ppm ÷ 1,000 = 340 ppt

Step 3 – Verify the Result

After performing the division, you will have the concentration expressed in parts per thousand. In the example above, the CO₂ concentration is 340 ppt.

Step 4 – Convert Back to ppm (if needed)

To revert from ppt to ppm, multiply the ppt value by 1,000. For instance, 4,000 ppt of sediment in water equals:

4,000 ppt × 1,000 = 4,000,000 ppm

These simple arithmetic steps allow you to switch between ppm and ppt with confidence, ensuring accurate reporting in scientific and regulatory contexts.