Chlorine Dosing Calculator
Calculate exactly how much chlorine to add to your pool. Enter your pool volume, current and target free chlorine levels, and chlorine product type to get the precise dose.
Chlorine Product
Select the product you're adding. Liquid chlorine is the most common for quick dosing. Cal-Hypo granular is popular for regular maintenance. Trichlor tablets dissolve slowly in feeders or floaters.
The total water volume of your pool in gallons. Check your pool builder's paperwork, or estimate using: length × width × average depth × 7.48.
Your pool's current free chlorine level measured with a test kit or test strips. If you haven't tested yet, use 0.
The free chlorine level you want to reach. The ideal range for most pools is 2–4 ppm. A target of 3 ppm is a safe, practical goal for routine maintenance.
Chlorine to Add
Add with the pump running. Retest free chlorine after 4–6 hours once the product has fully circulated.
💡About this calculator▼
Maintaining free chlorine in the 2–4 ppm range keeps your pool sanitized and safe to swim in. This calculator tells you exactly how much chlorine product to add based on your pool size, your current reading, and the specific product you're using — whether that's liquid chlorine, Cal-Hypo granular, or trichlor tablets.
The calculator determines how many ppm of free chlorine need to be added (target minus current), then converts that into the weight of pure chlorine required for your pool volume. That pure chlorine requirement is then divided by the available chlorine percentage of your specific product to give you the exact dose.
If your current free chlorine is already at or above your target, the calculator will tell you no chlorine is needed.
📐How it's calculated▼
Amount = (Pool Volume ÷ 10,000) × 0.0834 lbs × ppm Increase ÷ Available Chlorine %
0.0834 lbs is the weight of pure chlorine needed to raise 10,000 gallons by 1 ppm.
Available chlorine by product:
• Liquid Chlorine (10%): ~10.9 fl oz per 10,000 gal per 1 ppm
• Liquid Chlorine (12.5%): ~8.75 fl oz per 10,000 gal per 1 ppm
• Cal-Hypo (65%): ~2.05 oz per 10,000 gal per 1 ppm
• Cal-Hypo (73%): ~1.83 oz per 10,000 gal per 1 ppm
• Trichlor Tablets (90%): ~1.48 oz per 10,000 gal per 1 ppm
• Dichlor (56%): ~2.38 oz per 10,000 gal per 1 ppm
📎Source: CDC Healthy Swimming — Pool Chemical Safety; standard pool chemistry calculations (0.0834 lbs pure chlorine per 10,000 gal per 1 ppm)
🔍Finding your inputs▼
Pool Volume: Check your pool builder's paperwork or equipment manual. If unavailable, estimate using: length × width × average depth × 7.48 for a rectangular pool.
Current Free Chlorine: Test your pool water with a test kit or test strips and enter the reading. If you haven't tested yet, enter 0 as a conservative starting point.
Target Free Chlorine: The level you want to reach. The CDC and most pool health guidelines recommend 1–3 ppm for residential pools. A target of 3 ppm gives you a comfortable buffer before the level drops below 1 ppm.
Chlorine Product: Select the exact product you're adding. The percentage refers to the available chlorine content — check the product label if unsure. Liquid chlorine is typically 10% or 12.5%. Cal-Hypo granular is 65% or 73%. Trichlor tablets are ~90%.
⚠️Special situations▼
Free chlorine is zero or pool has visible algae
If FC reads zero or you have visible algae, routine dosing is not enough — you need to shock the pool first. Shock raises FC to 10–30 ppm to break down contaminants and kill algae. After shocking and the FC drops back to 1–3 ppm, use this calculator for regular maintenance dosing.
Trichlor or dichlor driving CYA too high
Trichlor adds ~0.6 lbs of cyanuric acid (CYA) per lb of product. Dichlor adds ~0.9 lbs CYA per lb. If your CYA exceeds 80 ppm, chlorine becomes much less effective even at correct FC levels. Switch to liquid chlorine or Cal-Hypo (neither adds CYA) and partially drain and refill the pool to dilute CYA.
Cal-Hypo raising calcium hardness too high
Cal-Hypo adds calcium to the water with each dose. If your calcium hardness exceeds 400 ppm, you risk scale formation on the pool surface and equipment. If calcium is trending high, liquid chlorine (sodium hypochlorite) is a better choice — it adds no calcium.
Chlorine demand — adding chlorine but levels won't rise
If you've added the calculated dose but FC isn't rising, your pool likely has chlorine demand — organic contaminants, ammonia, or combined chlorine are consuming the chlorine as fast as you add it. Shock with a heavy dose (triple the normal shock amount), run the filter 24 hours, and retest before resuming routine dosing.
❓Common questions▼
What free chlorine level should I maintain?
The CDC recommends a minimum of 1 ppm free chlorine in residential pools and 3 ppm in hot tubs. Most pool professionals target 2–4 ppm as a practical range — high enough to sanitize effectively, low enough to avoid skin and eye irritation. If your pool uses cyanuric acid (CYA) as a stabilizer, you may need higher FC levels since CYA reduces chlorine's effectiveness.
What's the difference between liquid chlorine and Cal-Hypo?
Liquid chlorine (sodium hypochlorite) is fast-dissolving, easy to apply, and doesn't raise calcium hardness or CYA. It's ideal for pools with already-elevated calcium or CYA. Cal-Hypo (calcium hypochlorite) is a granular product that's more concentrated and shelf-stable, but adds calcium with each dose. Both are effective — the best choice depends on your water chemistry.
How often should I add chlorine?
Most pools need chlorine added every 2–5 days during the swim season, depending on sun exposure, usage, and temperature. Outdoor pools lose chlorine faster due to UV degradation — this is why cyanuric acid (CYA) is added as a stabilizer. Test your free chlorine at least twice a week and dose as needed to keep it in the 2–4 ppm range.
Can I add chlorine while people are swimming?
It's best to add chlorine when the pool is not in use and let it circulate for at least 30 minutes before swimming. Liquid chlorine can temporarily spike FC levels near the point of entry. Granular products should always be pre-dissolved or broadcast across the surface — never added directly to the skimmer.
Why is the dose different for 10% vs 12.5% liquid chlorine?
10% and 12.5% refer to the available chlorine concentration in the liquid. A 12.5% product is about 25% more concentrated than a 10% product, so you need less of it to add the same amount of chlorine. Using the wrong concentration in your calculation will result in under- or over-dosing — always check the label.
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