Home Pool Chlorine Calculator
Pool Chlorine Calculator — How Much Chlorine to Add
Estimate how much chlorine product to add from your pool volume, current free chlorine (FC), target FC, and product strength. For algae or a one-time superchlorination treatment, use the separate shock or SLAM tools.
💡 Quick answers — chlorine dose for a 1 ppm FC increase
10,000 gal: about 12.8 fl oz of 10% liquid chlorine | 10.2 fl oz of 12.5% liquid chlorine | 2.1 oz of 65% cal-hypo | 2.4 oz of 56% dichlor
20,000 gal: about 25.6 fl oz of 10% liquid chlorine | 20.5 fl oz of 12.5% | 4.1 oz of 65% cal-hypo | 4.8 oz of 56% dichlor
Metric: 10,000 L → about 100 mL of 10% liquid chlorine per 1 ppm FC increase.
Product strength and label directions vary, so use the calculator as an estimate and retest after the product has circulated.
⚠️ Follow the exact product label for addition method and swimmer re-entry. Never mix chlorine with acid or with another pool chemical.
Match the product to the calculation:
- Liquid chlorine — fast-dissolving; choose the concentration printed on the bottle
- 65% cal-hypo — granular unstabilized chlorine; also adds calcium
- Trichlor tablets — slow maintenance dosing through a compatible feeder; not an instant ppm correction
- Test kit — verify FC before dosing and after circulation
- FAS-DPD test kit — useful when you need a wider, more precise chlorine test range
Example calculation
A 20,000 gallon pool tests at 0.5 ppm FC and the chosen target is 2.0 ppm, so the required increase is 1.5 ppm.
| Input | Value |
|---|---|
| Pool volume | 20,000 gallons |
| Current FC | 0.5 ppm |
| Target FC | 2.0 ppm |
| Increase needed | 1.5 ppm |
| 10% liquid chlorine | about 38.4 fl oz |
| 65% cal-hypo | about 6.2 oz |
| 56% dichlor | about 7.2 oz |
These are concentration-based estimates. Actual products vary; follow the product label and retest FC after circulation.
Liquid chlorine dosage chart by pool size
How much liquid chlorine to add based on pool size and ppm increase needed.
| Pool size | +1 ppm (10%) | +1 ppm (12.5%) | +2 ppm (10%) | +3 ppm (10%) | +5 ppm (10%) |
|---|---|---|---|---|---|
| 5,000 gal | 6.4 fl oz | 5.1 fl oz | 12.8 fl oz | 19.2 fl oz | 32 fl oz |
| 10,000 gal | 12.8 fl oz | 10.2 fl oz | 25.6 fl oz | 38.4 fl oz | 64 fl oz |
| 15,000 gal | 19.2 fl oz | 15.4 fl oz | 38.4 fl oz | 57.6 fl oz | 96 fl oz |
| 20,000 gal | 25.6 fl oz | 20.5 fl oz | 51.2 fl oz | 76.8 fl oz | 128 fl oz |
| 25,000 gal | 32 fl oz | 25.6 fl oz | 64 fl oz | 96 fl oz | 160 fl oz |
| 30,000 gal | 38.4 fl oz | 30.7 fl oz | 76.8 fl oz | 115.2 fl oz | 192 fl oz |
Uses the same planning approximation as the calculator: 1 gallon of 10% sodium hypochlorite in 10,000 gallons raises FC by about 10 ppm; 12.5% uses 80% of the 10% volume. Product age and actual strength can change the real dose.
Cal-hypo chlorine dosage chart by pool size
Approximate amount of 65% available-chlorine cal-hypo required for a chosen FC increase.
| Pool size | +1 ppm | +2 ppm | +3 ppm | +5 ppm |
|---|---|---|---|---|
| 5,000 gal | 1.0 oz | 2.1 oz | 3.1 oz | 5.1 oz |
| 10,000 gal | 2.1 oz | 4.1 oz | 6.2 oz | 10.3 oz |
| 15,000 gal | 3.1 oz | 6.2 oz | 9.2 oz | 15.4 oz |
| 20,000 gal | 4.1 oz | 8.2 oz | 12.3 oz | 20.5 oz |
| 25,000 gal | 5.1 oz | 10.3 oz | 15.4 oz | 25.7 oz |
| 30,000 gal | 6.2 oz | 12.3 oz | 18.5 oz | 30.8 oz |
Calculated from pool water volume and 65% available chlorine. If your label lists a different strength, use its directions rather than this table.
Chlorine dosage in litres (metric pools)
If you measure your pool in litres, here's a quick conversion reference for liquid chlorine (10% sodium hypochlorite):
| Pool size | +1 ppm | +2 ppm | +3 ppm |
|---|---|---|---|
| 5,000 L | 50 mL | 100 mL | 150 mL |
| 10,000 L | 100 mL | 200 mL | 300 mL |
| 20,000 L | 200 mL | 400 mL | 600 mL |
| 40,000 L | 400 mL | 800 mL | 1,200 mL |
| 50,000 L | 500 mL | 1,000 mL | 1,500 mL |
Conversion: 1 US gallon = 3.785 litres. Based on 10% liquid chlorine. Formula: pool litres × ppm increase × 0.01 = mL of 10% chlorine needed.
Which type of chlorine should I use?
🏊 Liquid chlorine
Useful for a quick FC adjustment without adding calcium or stabilizer. Select 10% or 12.5% in the calculator to match the bottle.
⚗️ Cal-hypo granular
Useful when an unstabilized granular product is preferred. Check calcium hardness because repeated cal-hypo use adds calcium.
🧂 Dichlor granular
Dichlor is stabilized chlorine, so repeated use also adds cyanuric acid (CYA). Account for CYA when choosing an FC target.
💊 Trichlor tablets
Tablets dissolve slowly in a compatible feeder or floater and are intended for maintenance, not a precise instant ppm increase. Follow the tablet and feeder labels.
Chlorine product comparison
| Product | Typical listed strength used here | Also adds | Best calculator use |
|---|---|---|---|
| Liquid sodium hypochlorite | 10% or 12.5% | Primarily salt after use | Direct FC dose estimate |
| Calcium hypochlorite | 65% available chlorine | Calcium | Direct FC dose estimate |
| Dichlor | 56% available chlorine | CYA | Direct FC dose estimate |
| Trichlor tablets | Varies by product | CYA | Maintenance feeder dosing only |
The package label controls product-specific dosing and re-entry instructions. Never mix different chlorine products or chlorine with acid.
Chlorine tablets — why this calculator does not convert ppm to tablets
A 3-inch trichlor tablet is a slow-release maintenance product. Its actual delivery rate depends on tablet weight, feeder or floater setting, water flow, temperature, pump run time, and the product label. Treating a tablet as an instant fixed ppm dose can overstate the precision of the result.
If you select tablets above, the calculator will direct you to the feeder and product instructions instead of returning a made-up tablet count. Test FC regularly and adjust the feeder to maintain the target appropriate for your pool.
Trichlor is stabilized chlorine and contributes CYA over time. If CYA is already elevated, compare your FC target with the CYA/FC calculator and consider an unstabilized chlorine source.
Chlorine dosing tips
🧪 Test before and after dosing
Use a reliable free-chlorine test. Dose from the measured FC difference, circulate as directed by the product label, then retest before making another adjustment.
📊 Choose the FC target for your chemistry
CDC guidance for home pools is at least 1 ppm FC without CYA and at least 2 ppm when CYA or stabilized chlorine is used. The appropriate operating target can be higher; follow your sanitizer/product guidance and local rules.
☀️ Account for stabilizer
CYA changes chlorine behavior. This page calculates the amount of product needed for the FC increase you enter; it does not choose a CYA-based target for you.
⚠️ Keep chemicals separate
Never mix chlorine products with acid or with one another. Only predissolve a product if its label specifically directs you to do so.
Chlorine calculator FAQs
How much chlorine should I add to my pool?
Enter your pool gallons, current free chlorine, target free chlorine, and product strength. For a 10,000 gallon pool, raising FC by 1 ppm takes about 13 fl oz of 10% liquid chlorine, 2.1 oz of 65% cal-hypo, or 2.4 oz of 56% dichlor. Treat those as concentration-based estimates and follow the product label.
What free chlorine level should I target?
There is no single target that fits every pool. CDC recommends at least 1 ppm FC in pools without CYA and at least 2 ppm when CYA or stabilized chlorine is used. Use the target appropriate for your sanitizer system, CYA level, product instructions, and local requirements.
Why does CYA matter when choosing a chlorine target?
Cyanuric acid changes chlorine behavior and is also added by stabilized products such as dichlor and trichlor. This calculator lets you enter the FC target you have chosen; use the CYA/FC calculator when you specifically need a CYA-based target.
Can I calculate a precise dose from chlorine tablets?
No. Trichlor tablets dissolve slowly and their delivery rate depends on tablet size, feeder setting, water flow, temperature, and the product label. Use tablets for maintenance through a compatible feeder, test FC, and adjust the feeder rather than treating a tablet as an instant fixed ppm dose.
Can I use dichlor in a hot tub?
CDC recommends not using cyanuric acid or chlorine products with cyanuric acid in hot tubs. Follow the hot-tub sanitizer product label and your local guidance rather than transferring a pool dose directly to a spa.
How long after adding chlorine can I swim?
Do not rely on a universal wait time. Follow the specific product label and test the water before re-entry. Different chlorine products can have different instructions and upper residual limits.
Can I mix chlorine products or chlorine and acid?
No. Never mix chlorine products with acid or mix different pool chemicals together. CDC warns that incompatible pool chemicals can release toxic gases or react violently.
Is this calculator for routine chlorination or shocking?
This page is for a direct free-chlorine dose from a current FC to a chosen target. Use the Pool Shock Calculator for a deliberate shock or superchlorination dose and the SLAM Calculator for persistent algae using a CYA-based target.