Piper Diagram Maker: Free Online Piper Plot
Paste major-ion analyses in mg/L or meq/L and get a Piper plot that classifies each sample by water type. The milliequivalent percentages are worked out for you. Free, in the browser.
What a Piper diagram shows
A Piper plot is three diagrams in one. The lower-left triangle plots the major cations — calcium, magnesium, and sodium plus potassium. The lower-right triangle plots the major anions — chloride, sulphate, and bicarbonate plus carbonate. Each sample is then projected up into the central diamond, which combines both and is where the classification is actually read.
Crucially, the axes are milliequivalent percentages, not mg/L. Ions have to be converted by dividing concentration by equivalent weight before the proportions mean anything, because a milligram of sodium and a milligram of calcium do not carry the same charge. Paste raw mg/L and the conversion is done for you; a poor charge balance is flagged rather than quietly plotted.
Data
Paste straight from Excel or Google Sheets, or import a CSV or .xlsx file — columns are matched by name, in any order, and a workbook can bring one specimen per sheet.
| # | Sample(opt) | Group(opt) | Camg/L | Mgmg/L | Namg/L | Kmg/L(opt) | Clmg/L | SO4mg/L | HCO3mg/L | CO3mg/L(opt) | TDSmg/L(opt) | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | ||||||||||||
| 2 | ||||||||||||
| 3 | ||||||||||||
| 4 |
0 rows of data
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Export Piper + Stiff + Schoeller
Renders all three hydrochemical diagrams from the table above and downloads them as one zip.
Options
This plot has no adjustable options yet.
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How to read the diamond
Position in the diamond names the water type. Samples near the left corner are Ca–HCO₃ waters: typical fresh, recently recharged groundwater in a carbonate or silicate aquifer. Near the right corner are Na–Cl waters: seawater, evaporite dissolution, or old, deep, stagnant brine. The top is Ca–SO₄, which usually means gypsum or anhydrite dissolution, or mine drainage. The bottom is Na–HCO₃, the classic signature of a water that has been through cation exchange on clays.
The pattern across samples often says more than any single point. Samples strung out along a straight line in the diamond indicate simple mixing between two end members — freshwater and seawater in a coastal aquifer, for instance — and the position along that line estimates the mixing fraction. A curve away from the mixing line means a reaction is happening as well: ion exchange, dissolution, or sulphate reduction.
Who uses one
Hydrogeologists mapping hydrochemical facies and flow paths, environmental consultants baselining groundwater monitoring networks, water utilities tracking source stability, and anyone investigating saline intrusion or leachate migration.
Common questions
- Should I enter mg/L or meq/L?
- Either. Enter mg/L — which is what a lab certificate reports — and the conversion to milliequivalents is done for you.
- What charge balance error is acceptable?
- Under 5% is normally considered good for a routine major-ion analysis; over about 10% suggests a missing ion or an analytical problem and the sample should be treated with suspicion.
Methodology
A methods paragraph to put beside the exported figure. It describes the tool’s default settings, so edit a clause if you changed one. References are given as the tool’s source code records them.
Major-ion concentrations were converted from mg/L to meq/L with the equivalent weights tabulated by Hem (1985) and Freeze & Cherry (1979), with values below the reporting limit taken as half that limit (Helsel, 2005). The charge-balance error was computed in the half-sum form and analyses beyond ±10 % were flagged. Cation (Ca, Mg, Na + K) and anion (HCO₃ + CO₃, SO₄, Cl) percentages of the meq totals were plotted on a Piper (1944) trilinear diagram and projected into the central diamond, and water types were named after Back (1966) from the ion group holding more than 50 % of each total.
References
- APHA Standard Methods 1030E.
- Back, W. (1966). Hydrochemical facies and ground-water flow patterns in northern part of Atlantic Coastal Plain. USGS Professional Paper 498-A.
- Freeze, R.A. & Cherry, J.A. (1979). Groundwater.
- Helsel, 2005.
- Hem, J.D. (1985). Study and Interpretation of the Chemical Characteristics of Natural Water. USGS Water-Supply Paper 2254.
- Piper, A.M. (1944). A graphic procedure in the geochemical interpretation of water-analyses. Transactions, American Geophysical Union 25(6), 914–928.
- StrataPlot. (2026). StrataPlot: Piper Diagram [Computer software]. https://www.strataplot.com/piper-diagram
How to cite this tool
If a figure made here goes into a report, thesis or paper, cite the tool so readers know how it was drawn. Add the date you accessed it if your style guide asks for one.
StrataPlot. (2026). StrataPlot: Piper Diagram [Computer software]. https://www.strataplot.com/piper-diagram
@misc{strataplot_piperdiagram,
author = {{StrataPlot}},
title = {StrataPlot: Piper Diagram},
year = {2026},
howpublished = {\url{https://www.strataplot.com/piper-diagram}},
note = {Computer software}
}