Fieldwynn
Fieldwynn
Search tools…

Pool Shock Calculator

How much shock for your pool — pick the chemical, strength %, and target (breakpoint, reason preset, or custom) and read the dose in pounds, ounces, or gallons.

Pool volume

US gallons — the dosing denominator. Not sure? Use the helper below.

Unit
Don't know your gallons?
Shape
Measure in

Full shape set in the Pool Volume Calculator.

Shock chemical

Available-chlorine %. Check the bag/jug label — it's the biggest lever on the dose.

Shock target
How to set the target
Current readings

From your kit. Leave blank if unknown — we'll target a 10 ppm shock.

Shock dose

—

Enter your pool volume and readings to see the shock dose.

Target free chlorine
—
Raise FC by
—
Export
How this is calculated

Shock dosing is an available-chlorine mass balance: the product amount scales with your pool volume, with how far you need to raise free chlorine (Δppm), and inversely with the product's available-chlorine %. 

combined chlorine (CC) = total chlorine − free chlorine   (breakpoint mode)

target FC, by basis:
  breakpoint:  10 × CC      (the 10:1 breakpoint rule; 10 ppm if TC unknown)
  reason:      routine 10 · opening 15 · light algae 20 · heavy algae 30 · after-rain 15
  custom:      the FC ppm you enter

Δppm = max(0, target FC − current FC)

dose = Δppm × (volume / 10,000) ÷ (ppm-per-unit × strength factor)
     ≈ cal-hypo 65%  2.05 oz per ppm per 10k
     ≈ liquid 10%    12.8 fl-oz per ppm per 10k

Strength is the biggest lever. A 12.5% jug of liquid raises FC faster than a 10% jug, so the same dose target needs less product — the tool divides the dose by your entered strength relative to each chemical's reference (cal-hypo 65%, liquid 10%, dichlor 56%, lithium 35%).

This is a shock dose, not maintenance. Our cal-hypo basis is the better-corroborated shock figure (about 7.8 ppm FC per pound of 65% cal-hypo in 10,000 gallons — Larry's Pool's "≈ 20 oz for +10 ppm" and Omni's coefficient), which differs slightly from a routine-maintenance basis. Treat the number as a starting dose and re-test with your kit.

Chlorine is not always the limiting factor. Where algae keeps returning within days of a shock, the water is usually feeding it, and the phosphate remover and algaecide dose calculator sizes the side of the treatment that starves the bloom instead of burning it off. A full green-water recovery is a multi-day protocol rather than a single dose, which the green pool recovery calculator lays out.

Sources: Omni Calculator — Pool Shock Calculator (breakpoint math + safety envelope); Larry's Pool — Pool Shock Calculator (five chemistries + CC-unknown fallback); The Pool Nerd — Pool Shock Calculator (reason → target ppm).

Frequently asked questions

How much shock does a 15,000 gallon pool need?
For a routine 10 ppm shock from zero free chlorine, about 30.8 oz of 65% cal-hypo — 1 lb 15 oz, near enough two pounds. The same job in 10% liquid chlorine is 192 fl oz, or 1.5 gallons. Those are the figures the calculator above returns; change the volume, the strength, or your current free-chlorine reading and they all move, because the dose is driven by the gap to the target rather than by the pool size alone. Your product label governs the actual dose.
Does the strength percentage really change the dose?
More than anything else on the page, which is why it is editable for every chemical rather than hard-coded. Cal-hypo sold at 73% available chlorine needs about 11% less product than the same job at 65% — 27.4 oz against 30.8 oz on the 15,000-gallon example above. Liquid chlorine at 12.5% needs a fifth less than a 10% jug. Dose what is actually on the truck: read the percentage off the bag or jug and type it in.
What is breakpoint chlorination and how is the target worked out?
Combined chlorine is what is left when chlorine has bound to ammonia and nitrogen compounds — it is the chloramine smell, and adding a little more chlorine makes it worse rather than better. Breakpoint is the point where you have added enough to burn it off. The arithmetic is combined chlorine = total chlorine − free chlorine, then target = 10 × combined chlorine, the well-established 10:1 rule. A reading of 5.0 ppm total against 3.0 ppm free is 2.0 ppm combined, so the target is 20 ppm — a 17 ppm raise. Leave total chlorine blank and the calculator targets a sensible 10 ppm instead.
Does non-chlorine shock (MPS) work for breakpoint?
No, and the calculator refuses to pretend otherwise: pick MPS on a breakpoint or custom free-chlorine target and it returns no chlorine dose at all, with a note saying why. Potassium monopersulfate is an oxidiser — it burns off organic load without raising free chlorine, so it cannot satisfy a target expressed in free-chlorine ppm. It is offered under the oxidiser presets only, dosed by its own label.
Does a saltwater pool still need shocking?
Yes. A salt cell generates chlorine steadily for day-to-day demand; it is not built to deliver a breakpoint dose on demand, and running it harder to try is how cells get worn out early. Shock a salt pool with the same products and the same arithmetic as any other — this calculator sizes it. Keeping the cell fed is the separate job: the pool salt calculator works out how much salt takes the water to the cell's target ppm, in pounds and 40 lb bags or kilograms and 25 kg bags.

Sources

  1. Pool Shock Calculator. Omni Calculator. Retrieved .
  2. Pool Shock Calculator. Larry's Pool. Retrieved .
  3. Pool Shock Calculator. The Pool Nerd. Retrieved .

How we choose and check our formulas

Get early access

Fieldwynn is the field-first app we are building for small crews — simple in the truck, powerful in the back office. It is not out yet; join the early-access list and be first when it launches for your trade.