Garden & outdoor
How much chlorine does your pool need?
Free pool chlorine calculator: grams and tablets for maintenance, shock or season opening from pool volume in m³.
Quick answer
Pool chlorine is dosed per cubic metre of water — not per bag on instinct. Formula: **chlorine (g) = volume (m³) × dose (g/m³)**. A **40 m³** family pool on **maintenance** at **2 g/m³** needs **80 g** of active chlorine — roughly **one 200 g trichlor tablet at 90%** for that application. **Shock** after green water or heavy rain runs **10–15 g/m³** (480 g active chlorine on 40 m³) — a different product and a different day than weekly tablets.
Advanced settings
Active chlorine needed
80 g
- Product to add
- 89 g
- Tablets (rounded up)
- 1
- Water volume used
- 40,000 L (40 m³)
⚠️ Indicative doses only — always follow the product label and never mix pool chemicals together.
Formula: chlorine (g) = volume (m³) × dose (g/m³). Tablets = round up to active chlorine ÷ (tablet weight × chlorine %). Target free chlorine 1–3 ppm for maintenance; shock after rain, algae or heavy use. Test pH (7.2–7.6) before dosing.
How it works
Start from your volume: if you only know length and width, use our pool volume calculator first. Then pick maintenance, shock or season opening, adjust product % and tablet size in advanced settings, and verify with pool test strips — free chlorine 1–3 ppm, pH 7.2–7.6.
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Frequently asked questions
How much chlorine for green pool water?+
Green water needs shock chlorination, not maintenance tablets: typically 10–15 g/m³ of active chlorine (select Shock in the calculator), brush walls, run the pump 24–48 h, then backwash the filter. Correct pH to 7.2 first — high pH makes chlorine ineffective. If it greens again within days, test cyanuric acid stabilizer.
How often should I add chlorine?+
Maintenance dosing is usually weekly in season (slow tablets in a floater or skimmer), but heatwaves and heavy bathing can double consumption. Measure free chlorine 2–3 times per week with test strips — dose to stay at 1–3 ppm, not on calendar autopilot.
Tablets or granular chlorine?+
Slow trichlor tablets (200 g, ~90% active) suit steady maintenance in a dispenser. Fast-dissolving granules or shock powder are for superchlorination — never crush tablets into the skimmer for a shock dose. Enter your product's chlorine % in advanced settings; multi-action tablets often show lower active % than pure trichlor.
How do I know my pool volume in m³?+
Rectangular: length × width × average depth. Round: π × (diameter ÷ 2)² × depth. Average depth is halfway between shallow and deep end. A 7 × 3.5 m pool at 1.4 m average depth holds about 34 m³ (34,000 L). Use the dimensions mode here or the dedicated pool volume calculator for pump sizing too.
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