Calculators
Sizing calculators for home water treatment: grain capacity, flow rate, micron rating and more, with the formula shown.
Inputs you already have, one formula, one answer. Every calculator shows its working and names the source the formula came from, so you can check it rather than trust it.
Well pump size calculator: GPM from your fixture count, capped at the well's yield, with the pump type for your depth
Pump gpm = fixtures x 1 gpm (Water Systems Council, Red Lion): an 8-fixture house takes an 8 gpm pump, never above the well yield, submersible past 90 ft.
Water distiller cost per gallon calculator: kWh, electricity cost and hours per gallon or litre
kWh per gallon = watts x hours per batch / gallons. An 800 W distiller at 4 hours a gallon uses 3.2 kWh, about 59 cents at EIA's July 2026 18.31 cents per kWh.
Softened water sodium calculator: milligrams per glass and per day from your hardness number
Sodium added = 8 mg/L per gpg of hardness removed (NDSU). 15 gpg softened water carries 120 mg/L: 28 mg per 8 oz glass, 240 mg in 2 L a day.
Water filter cartridge life calculator: how many days a filter lasts from its gallon rating, your daily use and the maker's month cap
Days = rated gallons / gallons per day, capped by the maker's months. A 40-gallon, 2-month Brita Standard at 0.5 gal/day lasts 60 days, not 80.
Well shock chlorination bleach calculator: casing gallons, target ppm and cups of bleach
Casing gallons = 0.041 x diameter squared x feet of water. A 6-inch well with 100 feet holds 148 gal and takes about 4 cups of 6% bleach at 100 ppm.
Acid neutralizer size calculator: calcite or Corosex tank size from pH and peak flow
Bed area = peak gpm / 5 for calcite (pH 6.0-7.0) or / 3 for a calcite-Corosex blend. A 2.5 gpm home at pH 6.8 needs a 10x54 tank and 98 lb of calcite.
Iron filter size calculator: the largest tank your well pump can backwash for Birm, GreensandPlus or Katalox Light
Largest tank = pump GPM divided by the media backwash rate. A 10 GPM pump backwashes a 12-inch Birm tank (9.4 GPM needed) and stalls on 13-inch (11.1 GPM).
Micron rating picker: which sediment filter micron for grit, haze, cysts, RO or UV
Coarse to fine: a 700 to 15 micron screen, then a 5 micron cartridge (NDSU: 10 to 15 micron for a drilled well, 2 for a dug well), absolute 1 micron for cysts.
Reverse osmosis GPD and tank size calculator: real output from pressure, temperature and people
Effective GPD = rated GPD x (psi / 60) x (1 + 0.015 x (F - 77)). A 75 GPD unit at 50 psi, 60 F makes about 47 GPD from a 3.2 gal tank. Calculator.
Softener resin volume to grain capacity calculator: cubic feet, salt dose and tank size
Usable grains = resin cu ft x grains per cu ft at the salt dose. 1.0 cu ft of 8% resin gives 20,000 grains at 6 lb, 24,000 at 10 lb. Calculator and tank table.
UV water purifier size calculator: GPM at NSF/ANSI 55 Class A dose from bathrooms
Peak gpm = bathrooms x 2.5 + 2.2; a 2-bath house pulls 7.2 gpm. Size to the 40 mJ/cm2 Class A rating: a VIQUA VH410 sold as 18 GPM is 14 gpm at that dose.
Water hardness unit converter: gpg, mg/L, ppm, dH, fH, Clark and mmol/L
1 gpg = 17.118 mg/L as CaCO3, 1 dH = 17.848, 1 fH = 10, 1 Clark = 14.254, 1 mmol/L = 100.09. Convert any hardness unit to the others and read the USGS band.
Water softener salt usage calculator: pounds per regeneration and bags per year
Salt per regeneration = resin cu ft x dose (6, 10 or 15 lb/cu ft). A 1 cu ft unit at 10 lb, 4 people, 10 gpg uses about 406 lb a year: ten 40 lb bags.
Water softener size calculator: grain capacity from people, hardness and iron
Grains = people x 75 gal/day x (gpg + 5 per mg/L iron) x days between regenerations. 4 people at 10 gpg for 7 days is 21,000 grains. Calculator and the size table.
Whole-house filter flow rate calculator: GPM from fixtures and bathrooms
Peak gpm = showers running at once x 2.5 + one faucet at 2.2, or WQA fixture units x 0.4 + 2. A 2-bath home pulls about 7 gpm; a 20 x 4.5 in housing is rated to 15.