Calculators
Quick answer
16 calculators for home water treatment. Every one shows its formula on the page, labels each figure as a published standard, a rule of thumb or something that only comes off your own water test, and returns "not published" rather than an estimate where no published figure exists.
Three rules apply to all of them, and they are the reason this site exists. The working is visible, so you can check it against your own laboratory report rather than trusting a black box. Every number declares its basis, because a published resin capacity and the eighty gallons per person per day sizing convention look identical in a results table and are not remotely equivalent. And where nobody publishes a figure, the answer says so: we print no generic water volume per regeneration and no generic pressure drop, because in both cases a single number would be wrong for most installations.
There is a fourth rule underneath those. Every one of these calculators is arithmetic on a number you have to measure. On city water your utility publishes a Consumer Confidence Report every year at no charge. On a private well only a certified laboratory test tells you what you have. Arithmetic on a guess is a guess.
Softener sizing and salt
- Water Softener Sizing Calculator The grain capacity your house actually needs, from your measured hardness and household size, with the nameplate size that lands on. The number on the box is the capacity at maximum salt dose, not a working figure.
- Water Hardness Converter Grains per gallon to milligrams per liter and back, at the published conversion of 17.1, with the USGS classification your result falls into. Laboratories report in ppm and equipment is sized in grains, which is where most of the confusion starts.
- Daily Hardness Load Calculator How many grains of hardness your household removes every day, including the compensation for dissolved iron and manganese that a softener also exchanges. This is the figure every other softener answer is built on.
- Water Softener Salt Calculator Salt per regeneration, per year, and what it costs, at your chosen salt setting. The efficient setting uses less than half the salt for about two thirds of the capacity, which is the trade nobody explains at the point of sale.
- Regeneration Frequency Calculator Days between regenerations for your size, hardness and household, against the three to fourteen day window that keeps a resin bed healthy without wasting salt.
- Resin Volume Calculator The resin volume behind any nameplate rating, and what that volume genuinely delivers at each salt dose, from the published resin exchange capacity curve.
Filtration and flow
- Whole House Flow Rate Calculator Peak gallons per minute from your fixture count, which is what a whole house filter has to pass. Undersizing here is the reason people blame a new filter for killing their water pressure.
- Sediment Filter Micron Selector The staging your water source actually needs, coarse to fine, and the difference between a nominal and an absolute rating. Going straight to one micron on silty water plugs the cartridge in days.
- Filter Cartridge Life Calculator How long a rated cartridge lasts at your household use, and why the real change trigger is a ten to fifteen pound rise in pressure drop rather than the calendar or the gallons.
Reverse osmosis
- Reverse Osmosis Production and Drain Ratio Calculator Real daily output from a rated membrane at your own feed pressure and water temperature, plus the gallons to drain per gallon produced. The rating on the box is measured at 60 psi and 77 degrees, which is not your kitchen.
- Reverse Osmosis Tank Drawdown Calculator What a nominal tank size actually delivers, which is roughly sixty to seventy percent of the number on the label, and the air charge that has to be set with the tank empty.
Well water treatment
- UV Dose Calculator The dose a system delivers at your actual flow rate, against the NSF/ANSI 55 Class A figure of 40 mJ/cm2 and the Class B figure of 16. Dose falls in proportion as flow rises, which is how an undersized system fails silently.
- Iron Treatment Selector Which class of equipment suits your measured iron level and the form the iron is in, because clear water iron, red water iron and iron bacteria need three different machines and only one of them is a filter.
- Acid Neutralizer Sizing Calculator Which neutralizing media suits your measured pH, and the hardness a calcite bed adds as it works, which changes how the softener behind it has to be sized.
Household use and cost
- Household Water Use Calculator Daily use for your household, at both the measured indoor figure from published end use studies and the conservative figure the trade sizes softeners on, so you can see how much of the difference is padding.
- Cost Per Gallon Calculator What filtered water actually costs per gallon once equipment and cartridges are counted, against what bottled water costs for the same volume.
Researched, not professional advice. These calculators work arithmetic on the numbers you give them. Your own water test is the authority, not any chart on this site. Nothing here diagnoses a water problem or says a product makes water safe to drink. Bacteria, nitrate, lead, arsenic and PFAS are not do it yourself topics: they are invisible and tasteless, and they need a certified laboratory and usually a licensed professional rather than a calculator and a product.