Compost Tea PPM Estimator
Compost tea strength is guesswork without a meter — but a quick EC reading converts to a rough PPM that tells you whether the brew is weak, good, or overdone.
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Compost Tea PPM Estimator
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Compost tea strength is guesswork without a meter — but a quick EC reading converts to a rough PPM that tells you whether the brew is weak, good, or overdone.
How to use this calculator
- Brew 24–36 hours with aeration.
- Measure EC.
- Convert to approximate PPM.
The formula
Rough 500-scale estimate; teas vary, so treat as a guide.
What the units mean
µS/cm — microsiemens per centimeter, the unit of electrical conductivity (EC) that meters actually measure before converting to a PPM estimate.
PPM (parts per million) — one part of solute per million parts of the total mixture. The workhorse unit for trace concentrations in water, air, and food.
Worked example
EC 800 µS/cm → ~400 PPM — a reasonable finished tea.
Quick reference
| EC | ≈ PPM | Verdict |
|---|---|---|
| 400 | 200 | Weak |
| 800 | 400 | Good |
| 1,400 | 700 | Strong |
Rough guide only.
Where you will actually use this
Over-strong teas can harm seedlings; weak teas waste the effort.
- Garden brewing
- Biological programs
Mistakes that give wrong answers
- Treating the estimate as precise
- Using anaerobic (smelly) tea
Key takeaways
- Formula: PPM ≈ EC × 0.5 (rough estimate for teas)
- Remember: Rough guide only.
- Watch out for: Treating the estimate as precise
- Next step: run your own numbers in the calculator above, then verify with a measurement — calculated values are only as good as the inputs.
Frequently asked questions
What PPM should compost tea be?
Roughly 200–600 PPM finished.