How to use this tool

Pick your state — see whether your corner of the country typically runs soft or hard, and what that band means in mg/L and grains per gallon.
Enter your number — from a lab report or a test strip, in either unit. Add iron if your report lists it; it changes the softener math.
Get the verdict — the USGS category for your number, whether a softener is usually worth it, and the size the industry-standard math calls for.

Honest limits

State typicals are geology, not your well. Hardness follows local rock, so water can differ a lot within a state — the map-derived typical is a starting point for curiosity, not a number to buy equipment from. The underlying USGS map is stream-water data from the 1975 water year: a picture of regional geology, not a well test.
This sizes softeners, not treatment plans. Bacteria, nitrate, arsenic, and lead — the health questions — are separate tests with separate fixes. Hardness is the nuisance question: scale and soap.
Salt-free “softeners” don't change your number. Template-assisted crystallization (TAC) conditioners reduce scale formation but leave the hardness minerals in the water — a test still reads hard afterward. If you want the number down, only ion exchange does that.
Softening adds sodium. Ion exchange swaps calcium and magnesium for sodium (or potassium). That matters on a sodium-restricted diet — a potassium-chloride-regenerated softener is the workaround.
Iron is a sizing input, not a treatment plan. A softener handles small amounts of dissolved iron; oxidized iron (rust-colored water) fouls the resin — iron filtration goes before the softener.

Frequently asked questions

My state shows “very hard” — do I need a softener?

Not necessarily — the state picture is typical geology, and your well is its own well. It's also not a health call: hardness is a nuisance issue (scale, soap scum, spotty dishes), not a contaminant. Industry guidance says a softener is worth considering above about 7 grains per gallon (120 mg/L), and the case is strong above 10.5 gpg (180 mg/L). Below 3.5 gpg (60 mg/L), softening is usually unnecessary.

What size softener do I need?

The industry-standard math: multiply your household size by 75 gallons per person per day, then by your hardness in grains per gallon (plus 5 gpg for each ppm of iron) — that's your daily grain load. Size the smallest standard unit (24,000 to 64,000 grains) that covers about a week, so the unit regenerates roughly every 5 to 7 days. The sizer above runs exactly that math.

Will a salt-free conditioner fix my hard water?

Not the way a softener does. Salt-free systems (usually template-assisted crystallization, or TAC) change how minerals behave so they form less scale — but they don't remove calcium or magnesium, so your water still tests hard and soap still lathers poorly. If the number itself bothers you, only an ion-exchange softener lowers it.

Does a water softener make well water safe to drink?

No. A softener removes hardness minerals and nothing else — bacteria, nitrate, arsenic, and lead pass through unaffected. If you haven't tested for the health parameters, do that first; a softener is a comfort and appliance-protection decision, not a safety one.

Why does hardness vary so much within a state?

Hardness is set by the rock your water moves through. Limestone and dolomite country — much of the Midwest, Texas, and the Southwest — dissolves calcium and magnesium into groundwater; granite and volcanic rock — New England, the Pacific Northwest — give up almost nothing. The USGS found hard well water concentrated in the east-central and western states, following the carbonate aquifers.

Will softened water taste salty?

Barely — the sodium added is small, roughly proportional to the hardness removed. It matters mainly on a sodium-restricted diet; a softener regenerated with potassium chloride instead of sodium chloride is the standard workaround, and NSF/ANSI 44 certification covers both.

Sources

USGS Water Science School — Hardness of Water — what hardness is (dissolved calcium and magnesium) and the four classification bands: soft 0–60, moderately hard 61–120, hard 121–180, very hard over 180 mg/L as CaCO₃
USGS — Map of water hardness in the United States — the per-state typical categories in this tool: mean hardness as calcium carbonate at NASQAN monitoring sites, 1975 water year (Briggs & Ficke 1977, USGS Open-File Report 78-200), edited by USEPA 2005
USGS — Quality of Water from Domestic Wells in the United States — hardness is a nuisance, not a health concern (scale in plumbing/fixtures/water heaters, poor soap performance); hard water tracks carbonate aquifers in the east-central and western states
WHO — Guidelines for Drinking-water Quality, hardness fact sheet — no health-based guideline value proposed for water hardness
NSF International — NSF/ANSI 44 technical requirements — the certification standard for residential cation-exchange softeners (hardness reduction, material safety, softening capacity; sodium or potassium chloride regenerant)
Industry-standard softener sizing — Crystal Quest, Quality Water Treatment, SoftPro Water Systems, home-water-softener.com — the method this tool computes with: 75 gallons per person per day, size for regeneration roughly every 5–7 days, standard residential sizes 24,000–64,000 grains, plus 5 gpg per ppm of iron
Salt-free conditioner caveat — Quality Water Lab (TAC explainer), Water Defense — “salt-free softeners” are conditioners: they don't remove hardness minerals, so water still tests hard

New to well water? Start with the well water hub. Reading a lab report? Run it through the Water Test Interpreter. Shopping for equipment? Read the treatment buyer’s guide first.