Bleach Dilution Calculator
Choose a mode to make a diluted solution, boost an existing batch, or blend two known batches — get exact water and bleach amounts instantly.
Worked examples
Mixing a 200 ppm surface sanitizer
A kitchen needs 10 liters of a 200 ppm chlorine sanitizing solution mixed from standard 5.25% household bleach.
- Final volume
- 10 L
- Target
- 200 ppm
- Bleach
- 5.25%
≈ 38.1 mL bleach + 9.96 L water
Blending two chlorinated batches
A pool operator combines a large lightly-chlorinated batch with a smaller freshly-shocked batch and needs the resulting strength.
- Batch 1
- 200 gal @ 3 ppm
- Batch 2
- 50 gal @ 12 ppm
≈ 250 gal at 4.8 ppm
How the formula works
Every mode on this page is the same idea applied differently: the amount of active chlorine in a batch is its concentration times its volume, and mixing two batches together doesn't destroy chlorine — it just spreads the combined amount across the combined volume. That's a mass balance: C₁·V₁ + C₂·V₂ = C_final·V_final. Making a fresh dilution is the special case where one side is plain water (concentration zero); increasing strength solves the same equation for the volume of bleach to add; mixing two known batches skips solving anything and plugs both sides in directly.
Frequently asked questions
Why do I need to know the bleach's percent available chlorine?
The percent on the label (usually 5.25%–8.25% for household bleach, much higher for pool-grade products) tells you how much active chlorine is packed into every bottle of stock solution. The dilution math scales directly with that number, so a bottle marked 8.25% needs less volume to hit the same target concentration than one marked 5.25% — using the wrong percentage is the most common source of an under- or over-strength mix.
Is it safe to mix bleach with other cleaning products?
No — never combine bleach with ammonia, vinegar, rubbing alcohol, or other acidic or ammonia-based cleaners. Bleach plus ammonia produces toxic chloramine vapors, and bleach plus acid produces chlorine gas; both can cause serious respiratory injury in an enclosed space. Always add bleach to water (not water to concentrated bleach), work in a ventilated area, and wear gloves and eye protection when handling concentrated stock.
Why does household bleach concentration vary between 5.25% and 8.25%?
Manufacturers reformulate for shelf stability and shipping weight, and "concentrated" or "ultra" lines are deliberately stronger than the classic 5.25% formula. Because the strength printed on the label directly changes how much stock solution you need, always check the current bottle rather than assuming a percentage from memory or an older container.
Does a diluted bleach solution stay effective indefinitely?
No. Once diluted, available chlorine breaks down steadily — most guidance treats a diluted solution as noticeably weaker after about 24 hours, faster if it's stored warm or in direct light. Mix only what you'll use in a work session and make a fresh batch next time rather than relying on a diluted bottle from days earlier.
What's the difference between the three modes on this page?
"Make" starts from plain water and figures out how much bleach to add to hit a target strength in a chosen final volume. "Increase" starts from a batch that already has some chlorine in it (even a previous dilution) and calculates how much additional bleach raises it to a higher target. "Mix" takes two batches you already know the volume and strength of and works out what you get when you pour them together — no target, just the forward result.
Can I use this for pool or spa chlorination instead of surface disinfecting?
The underlying mass-balance math is the same, so it works as a starting estimate. Real pool dosing also depends on factors this calculator doesn't model — pH, stabilizer (cyanuric acid) level, sunlight exposure, and bather load — so treat the result as a first approximation and confirm with test strips or a test kit before and after dosing.
Why did the calculator show an error instead of a result in Increase mode?
Increase mode requires two things to be physically possible: the target concentration must be higher than what the batch already has (otherwise you'd be diluting, not strengthening — use Make or just add plain water), and the bleach you're adding must be stronger than the target you're aiming for (you can't reach 500 ppm by adding a 300 ppm source, no matter how much you add). The error message tells you which condition failed.