How this calculator works
You type grains per gallon. The engine converts and classifies:
mg/L as CaCO3 = gpg × 17.1
< 1.0 gpg soft
1.0 to 3.5 gpg slightly hard
3.5 to 7.0 gpg moderately hard
7.0 to 10.5 gpg hard
over 10.5 gpg very hardUSGS publishes four mg/L bands: soft 0-60, moderately hard 61-120, hard 121-180, very hard above 180. Those cut at about 3.5, 7.0 and 10.5 gpg. The extra "slightly hard" slice under 3.5 gpg is so a 2 gpg report is not called the same "soft" as 0.2. It is still USGS-shaped, not a second scale, and it is not a ZIP lookup.
If gpg is missing, the result is a prompt to type the number. We will not fill it from a map.
What each input means
| Input | What it is actually asking |
|---|---|
| gpg | Grains per gallon as calcium carbonate, from a consumer confidence report or a lab. If you only have mg/L or ppm as CaCO3, divide by 17.1. A strip kit is a last resort. A ZIP is not an input, on purpose. |
Worked examples
Including one where the naive answer misleads, which is the example most calculators leave out.
Eight grains from a CCR
gpg 8. Band hard (7.0 to 10.5 gpg). Conversion 137 mg/L as CaCO3 (8 × 17.1, rounded). That is the case the engine is tested on. It is a class, not a shopping list. Soap and scale are real; a softener is a separate purchase you may or may not want.
A well report in mg/L
The lab prints 50 mg/L as CaCO3. 50 ÷ 17.1 ≈ 2.9 gpg. Type 2.9. Band slightly hard (1.0 to 3.5 gpg). Using the city CCR for a house on a well is the error this example exists to catch. EPA private-well pages are the other document. Type the lab that sampled this tap.
The one where a ZIP map misleads
A hardness map of the United States, or a "enter ZIP, we know your water" widget, saying the county is very hard, so you must buy a softener. A city that blends surface water in spring and wells in August can move a band in one season. A neighbour on a well is not the city. This form will not take a ZIP. If you do not have a number, get the CCR or a lab. Treating "hard" as a medical or code requirement to soften is the other failure. USGS classification is not a prescription.
What changes the result
The number is the whole input. Crossing 3.5, 7.0, or 10.5 gpg changes the label. It does not change a heater, a pipe, or a bid by itself.
A lab that reports "as CaCO3" and a kit that reports "total hardness" as a colour can disagree. Prefer the lab or the CCR, and stay in one unit when you convert.
Nothing on the form asks about taste, spots on glass, or an anode. Those are real and they are off this classifier. Spots are not a gpg, and gpg is not a reason to skip a leaking tank body.
Local considerations
Hardness is local because geology and the actual source are local. That is the reason a ZIP table is the wrong localiser: it pretends the postcode is the aquifer. The local data is the CCR for this system, or a lab for this well.
Utilities are required to issue a consumer confidence report. They are not required to put hardness on it. If it is missing, ask them or test. Do not paste a neighbouring town's number.
When not to use this
Do not use this as a ZIP lookup, a softener specification, or a health finding. Hardness is not a regulated contaminant on this page.
Do not use a map of the United States as the input. Type the report.
Do not use a "hard" result as a reason to replace pipes or a heater. Material is a look. A leaking tank is a replace. Those tools are separate.
HyrePlumber does not sell softeners, test water, or perform plumbing work. Matching is still being built.
Related on this site
- Pipe material on the homepage Copper pinholes in some chemistries. Hardness is one input, not a diagnosis.
- Water heaters Sediment and anodes. Scale is maintenance, not this class.
- Location is more local than it looks Water chemistry is on that list. The CCR is the document, not a ZIP tool.
- Find a plumber An enquiry, not a softener sale.
Questions this calculator answers
- How hard is my water?
- Whatever the CCR or a lab says, in grains per gallon or mg/L, classified on the bands below. We do not look up your ZIP. A city can have two sources, and a well is not the city map. Type the number from a report that is about this tap.
- Where do I find grains per gallon?
- Many consumer confidence reports list hardness as mg/L or ppm as calcium carbonate. Divide by 17.1 to get gpg, or type gpg if the report already uses grains. A well is a lab, not the city CCR. Test kits exist; a lab number beats a strip if you are making a decision.
- What are the USGS bands?
- USGS classifies 0 to 60 mg/L as soft, 61 to 120 as moderately hard, 121 to 180 as hard, and more than 180 as very hard, as calcium carbonate. In grains, that is about 0 to 3.5, 3.5 to 7, 7 to 10.5, and over 10.5 gpg. This form also labels 1.0 to 3.5 gpg as slightly hard so a 2 gpg CCR is not lumped with rainwater. That extra slice is a convenience on top of USGS, not a second science.
- Why will you not look up my ZIP?
- Because hardness is geology and a specific source, not a postcode. Two houses on the same street can be city versus well. A utility can blend sources seasonally. A ZIP table would be a fake localiser, and this site will not ship one.
- Do I need a water softener?
- This page will not say yes. Hard water is a scale and soap conversation, not a health-code violation. Softeners have their own salt, drain, and sodium questions. Classification is not a prescription. HyrePlumber does not sell softeners.
- Does hard water ruin a water heater?
- Scale on the element or in the tank is a real maintenance item, and a spent anode is another. Neither is a hardness number on this form turning into a replace. Use the repair-vs-replace tool for a leaking tank, and a plumber or the manufacturer's maintenance sheet for flushing and anodes.
- Does hardness matter for tankless?
- Scale is why tankless quotes often include water treatment. That cost belongs in the installed line on the tank-vs-tankless tool, not as a hidden multiplier here. This page still will not prescribe a softener from a gpg.
- Is hardness in the consumer confidence report?
- Sometimes, as a secondary or unregulated line. Hardness is not a Safe Drinking Water Act maximum contaminant level. If your CCR omits it, call the utility or use a lab. EPA requires community systems to issue a CCR; it does not require this box to be on it.
- My report is in mg/L. What do I type?
- Divide mg/L as CaCO3 by 17.1, then type grains per gallon. 137 mg/L is 8 gpg. If the report used a different hardness method, stay with that lab's unit or ask them for gpg. Do not mix grains of something else with this box.
- Is well water on this form?
- Yes, if you type a lab number from that well. Do not type the city CCR for a house on a well. EPA has separate private-well guidance. This classifier does not know which you are on.
- Does HyrePlumber sell softeners or test water?
- No. HyrePlumber does not perform plumbing work, sell treatment equipment, or run a lab. Matching is still being built.
Sources and methodology
Figures dated 26 August 2026. Last reviewed .
- Hardness of water (U.S. Geological Survey, Water Science School, retrieved 2026-08-26. Cited for the four mg/L classes (soft 0-60, moderately hard 61-120, hard 121-180, very hard over 180 as CaCO3). This form adds a slightly-hard slice at 1.0-3.5 gpg. Not a ZIP map.)
- Consumer Confidence Reports (U.S. Environmental Protection Agency, retrieved 2026-08-26. Cited as the annual water-quality report from a community system. Hardness may or may not appear. This page will not invent a ZIP in its place.)
- Private drinking water wells (U.S. Environmental Protection Agency, retrieved 2026-08-26. Cited because a well is not the city CCR. Type a lab number for that well.)
Related
- Pipe material by year built Copper pinholes are chemistry plus material. Year is a prior. Look at the pipe.
- Water heater repair vs replace Scale is maintenance. A leaking tank body is still a replace.
- Tank vs tankless payback Put treatment in the tankless installed cost if it is on the quote.
- Water usage calculator Gallons of habit. Hardness is not gallons.