Free Calculator · Published October 2026
Chlorine Dose Calculator: Shock Dose by Well Casing
Enter casing diameter and the standing water column. You get gallons in the well and the unscented bleach for a one-time shock at the ppm you pick.
Built by SubcontractorHub — the software plumbing contractors use to quote, finance, and run every job.
Book a DemoChlorine Dose Calculator for One Shock, Not a Pump
This chlorine dose calculator is the bleach for a shock. Continuous feed for iron or sulfur is the chlorine injection system sizing calculator. Do not use one page to answer the other question.
Standing water is the column in the casing, not the depth the driller wrote on the log.
Common residential casings are 4, 5, or 6 inches. Measure the inside, not the hole diameter.
If you only know total depth, switch the first field and enter the static level too.
Leave 0 to dose the casing only. The shock article uses about 2 gallons as a planning add-on. Type that only if you want it.
50, 100, and 200 are planning choices dealers discuss. They are not a federal private-well mandate.
Read the jug. Unscented only. Splash-less and scented products are the wrong chemical.
📋 Important: All calculator results are ballpark estimates
All calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements. A health department procedure overrides this arithmetic.
What the Chlorine Dose Calculator Is Measuring
Standing water, not drilled depth
A 200 foot well with the water standing at 40 feet does not hold 200 feet of water. It holds the column from the static level to the bottom. Dose the dry casing and you over-chlorinate. Dose only the sticker depth when the well is half empty of water and you under-chlorinate. The chlorine dose calculator asks for that column on purpose.
Gallons per foot follow the inside diameter. A 4 inch casing holds less than a gallon per foot. A 6 inch casing holds more. The figure is the cylinder, not a brand of well. If the casing changes size, split the column and run the tool twice. The procedure around the number, including the hold and the flush, is how to shock a well.
The formula, and the field rule beside it
Bleach gallons equal the target ppm times the gallons of water, divided by the jug's percent times 10,000. That 10,000 is the planning conversion already used on this site for injection stock: one percent sodium hypochlorite is treated as about 10,000 ppm available chlorine. Change the percent and the pour changes. An 8.25 percent jug is not a 5.25 percent jug.
The shock article also prints a coarser rule, about 3 quarts of 5 to 6 percent bleach per 100 gallons, labeled there as roughly 200 ppm. This tool shows that quart count next to the formula so a dealer can see they are not the same instruction. Use the formula when you want the arithmetic. Use the article's table when you are following that page's shortcut. If the county publishes its own table, follow the county.
Worked examples
Same math as the form. The article column is the 3-quart rule on the same gallons, not a second official dose.
| Case | Casing water | Formula | Article rule |
|---|---|---|---|
| 6 in, 100 ft of water, 200 ppm, 5.25% | 146.9 gal | 2.24 qt | 4.41 qt |
| 4 in, 80 ft, plus 2 gal plumbing, 100 ppm, 8.25% | 52.2 gal | 0.26 qt | 1.63 qt |
| 6 in, 180 ft deep, static at 40 ft, 50 ppm, 6% | 205.6 gal | 0.69 qt | 6.17 qt |
How this chlorine dose calculator differs from injection sizing
- Shock is one pour. Injection is a pump that runs with the well.
- Shock uses casing volume. Injection uses daily gallons and contaminant demand.
- Shock targets a high ppm you choose, then you flush it out.
- Injection leaves a small residual and usually a contact tank.
- Carbon and softener resin should be bypassed for a shock. They are often part of the train after injection.
- A positive bacteria test after a shock is a well problem, not a reason to triple this dose forever. See coliform bacteria in well water.
What to write on the job ticket
Casing diameter, standing feet, extra gallons if you added them, target ppm, bleach percent, and the quarts you poured. Then the date you flushed and the date the lab bottle is allowed. A water treatment dealer who saves that note can explain a second positive without guessing which shortcut was used. Permanent disinfection, when shock will not hold, is a different design. The UV sizing calculator is that conversation, after the well itself is sound.
Frequently Asked Questions
How does a chlorine dose calculator size a well shock?
It measures the standing water in the casing, not the drilled depth. Gallons per foot come from the inside diameter. You can type the water column, or type total depth and the static water level and let the tool subtract. An optional gallon add-on covers the pressure tank and plumbing if you want them in the dose. Bleach volume is target ppm times those gallons, divided by bleach strength percent times 10,000.
Is this the same as a chlorine injection system?
No. Shock chlorination is one dose poured into the well, circulated, held, and flushed. A chlorine injection system feeds a small continuous dose every time the well pump runs, sized from iron, manganese, sulfur, and a residual. That continuous job is the chlorine injection system sizing calculator. Use this page only for the one-time shock volume.
Why does this bleach volume differ from the 3-quart shock rule?
The how-to-shock-a-well article publishes a field shortcut of about 3 quarts of 5 to 6 percent bleach per 100 gallons and calls that roughly 200 ppm. This calculator uses the stock formula shared with the injection tool, where 1 percent sodium hypochlorite is about 10,000 ppm. Those two descriptions do not land on the same concentration. The formula is the number this page returns. The quart rule is shown beside it so you can see the gap. A state health department table overrides both.
What bleach should I pour into a well?
Plain unscented sodium hypochlorite labeled for disinfection. No fragrance, no splash-less thickener, and no product that says it is safe for colors. Read the percent on the jug you actually have, because 5.25 percent, 6 percent, and 8.25 percent are not the same dose. Bypass carbon filters and the softener before you circulate. High chlorine ruins carbon and is hard on resin.
Does the calculator set the contact time?
No. It stops at volume and bleach. Hold time, flushing, and the follow-up bacteria test are the procedure on the shock article, not a second formula. A clear glass of water is not a passed test. Retest only after the chlorine is gone, or the lab can report a false negative.
Put the Dose on the Customer Record
Save the casing, the column, the bleach percent, and the retest date next to the well, not in a notebook that stays in the truck.
Get a Free DemoAll calculations are estimates based on historical information and should be verified by the user. This tool is provided as a free service for planning purposes only and is not a substitute for a professional assessment, a supplier quote, or applicable local code requirements. It does not size a continuous chlorine injection system and it does not set contact time.