ppm and ppb are defined as:
1ppm = 1/106 = 10-6
1ppb = 1/109 = 10-9
So
1ppm = 1000ppb
The number of parts-per million xppm is equal to the number of parts-per billion xppb divided by 1000:
xppm = xppb / 1000
Example: 7000ppb is equal to 7ppm:
xppm = 7000ppb / 1000 = 7ppm
| ppb | ppm |
|---|---|
| 1 | 0.001 |
| 10 | 0.01 |
| 100 | 0.1 |
| 1000 | 1 |
| 10000 | 10 |
| 100000 | 100 |
| 1000000 | 1000 |