Operator math, worked
How to calculate percent removal (BOD and TSS)
Percent removal shows how much of something a plant took out, like BOD or TSS. Subtract the amount leaving from the amount coming in, divide by the amount coming in, then multiply by 100.
Last reviewed 2026-08-04
The formula
percent removed = (in - out) / in x 100
The steps
Find how much was removed
Subtract the amount leaving (out) from the amount coming in (in). That difference is what got removed.
Divide by what you started with
Divide the amount removed by the in value, never the leftover.
Turn it into a percent
Multiply by 100 to change the decimal into a percent.
Worked example
BOD comes in at 200 mg/L and leaves at 20 mg/L. What percent was removed?
- Removed: 200 - 20 = 180
- Divide: 180 / 200 = 0.9
- Percent: 0.9 x 100 = 90%
Answer: 90% removed
Common questions
- Do I divide by the in or the out number?
- Always the in number, the amount you started with.
- Does this work for TSS too?
- Yes. The same steps work for BOD, TSS, or any before-and-after amount.
- Why multiply by 100?
- It turns the decimal into a percent, so 0.9 becomes 90%.