Free vs Total Chlorine Calculator
Work out combined chlorine (chloramines) from your free and total chlorine readings and estimate how much shock is needed to fix it.
Compare Your Options And Get Clear Answers
Work out combined chlorine (chloramines) from your free and total chlorine readings and estimate how much shock is needed to fix it.
Free vs Total Chlorine Estimator
Enter your numbers below for an instant estimate.
How It Works
Key concepts behind this calculator
Test Free Chlorine
Free chlorine is the active sanitiser still available to kill germs.
Test Total Chlorine
Total chlorine is free chlorine plus used-up chloramines.
Subtract
Combined chlorine = total minus free. Above 0.5 ppm, shock the pool.
Use As A Guide
Results are estimates based on your inputs. Check real quotes, rates and professional advice before deciding.
Chlorine Targets
Typical residential pool guidelines (check local rules).
| Reading | Target (ppm) | Too Low | Too High |
|---|---|---|---|
| Free chlorine | 1 β 3 | Algae risk | Irritation |
| Total chlorine | Close to free | n/a | Chloramines |
| Combined chlorine | Under 0.2 | Smell and irritation | Shock above 0.5 |
| Cyanuric acid | 30 β 50 | Chlorine burns off | Chlorine lock |
| Rule of Thumb | Combined under 0.5 ppm | Shock to 10Γ combined | Retest after 24 hours |
Free vs Total Calculator FAQ
Answers to common questions about this calculator.
Free chlorine is the active sanitiser. Total chlorine includes free chlorine plus combined chlorine, which has already reacted with contaminants.
Usually combined chlorine (chloramines) formed when chlorine reacts with sweat, oils and urine, not too much free chlorine.
Shock the pool using breakpoint chlorination, about 10 times the combined chlorine level, then retest.
No. This is an estimate. Follow product labels and local health guidance when treating pool water.