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.

Typical hardness in all 50 states

The same USGS national-map data the picker above uses, in plain text: each state's dominant hardness category, with the USGS band it falls in. Statewide typicals describe regional geology — your well is its own well, and hardness can differ a lot within a state.

State	Typical hardness	mg/L as CaCO₃	Grains per gallon
Alabama	Soft	0–60	0–3.5
Alaska	Moderately hard	61–120	3.5–7
Arizona	Very hard	over 180	over 10.5
Arkansas	Hard	121–180	7–10.5
California	Hard	121–180	7–10.5
Colorado	Very hard	over 180	over 10.5
Connecticut	Soft	0–60	0–3.5
Delaware	Soft	0–60	0–3.5
Florida	Soft	0–60	0–3.5
Georgia	Soft	0–60	0–3.5
Hawaii	Soft	0–60	0–3.5
Idaho	Very hard	over 180	over 10.5
Illinois	Hard	121–180	7–10.5
Indiana	Hard	121–180	7–10.5
Iowa	Very hard	over 180	over 10.5
Kansas	Very hard	over 180	over 10.5
Kentucky	Hard	121–180	7–10.5
Louisiana	Soft	0–60	0–3.5
Maine	Soft	0–60	0–3.5
Maryland	Soft	0–60	0–3.5
Massachusetts	Soft	0–60	0–3.5
Michigan	Hard	121–180	7–10.5
Minnesota	Very hard	over 180	over 10.5
Mississippi	Soft	0–60	0–3.5
Missouri	Very hard	over 180	over 10.5
Montana	Very hard	over 180	over 10.5
Nebraska	Very hard	over 180	over 10.5
Nevada	Very hard	over 180	over 10.5
New Hampshire	Soft	0–60	0–3.5
New Jersey	Soft	0–60	0–3.5
New Mexico	Very hard	over 180	over 10.5
New York	Hard	121–180	7–10.5
North Carolina	Soft	0–60	0–3.5
North Dakota	Very hard	over 180	over 10.5
Ohio	Hard	121–180	7–10.5
Oklahoma	Very hard	over 180	over 10.5
Oregon	Soft	0–60	0–3.5
Pennsylvania	Moderately hard	61–120	3.5–7
Rhode Island	Soft	0–60	0–3.5
South Carolina	Soft	0–60	0–3.5
South Dakota	Very hard	over 180	over 10.5
Tennessee	Hard	121–180	7–10.5
Texas	Very hard	over 180	over 10.5
Utah	Very hard	over 180	over 10.5
Vermont	Soft	0–60	0–3.5
Virginia	Soft	0–60	0–3.5
Washington	Soft	0–60	0–3.5
West Virginia	Moderately hard	61–120	3.5–7
Wisconsin	Hard	121–180	7–10.5
Wyoming	Very hard	over 180	over 10.5

States where the map shows a real split — the table lists the dominant category, and these notes describe the rest of the picture:

Arkansas: Mixed: soft (0-60) in the eastern Delta, very hard (181-250) in the northwest Ozarks; hard dominant elsewhere.
California: Mixed: soft in the north, hard through the Central Valley, very hard in the south.
Delaware: Small state; read at low confidence from the national map.
Hawaii: Small inset; read at low confidence from the national map.
Idaho: Extensive no-data (white) areas in the mountains alongside the dominant very-hard color.
Illinois: Mixed: very hard in the central part of the state, hard north and south.
Indiana: Mixed: very hard in the central part of the state, hard north and south.
Iowa: Mixed: very hard in the west, hard in the east.
Maryland: Small state; read at low confidence from the national map.
Minnesota: Extensive no-data (white) areas in the northern part of the state.
New York: Extensive no-data (white) areas in the Adirondacks alongside the dominant hard color.
North Dakota: Extensive no-data (white) areas in the northern tier.
Wisconsin: Extensive no-data (white) areas in the northern part of the state.

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.