Free Online Stereonet: Plot Planes, Poles, and Rose Diagrams
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One measurement per line, two numbers separated by a comma. Anything after the second number is treated as a note.
How to use this stereonet properly
Start by telling the tool what your two numbers mean, because this is where most stereonet mistakes are born. The default is strike and dip in the right hand rule, the convention where you walk along strike with the dip falling to your right, so 090/45 dips south. If your notebook records dip direction instead, switch the selector and enter 180/45 for that same plane. If you are plotting lineations, slickenlines, fold axes, or borehole trajectories, choose trend and plunge. Paste one measurement per line as two numbers separated by a comma, or load the CSV straight from our phone clinometer, which already writes the right columns in the right order.
Reading what appears
Each plane draws as a great circle, the curved line where the plane cuts the lower hemisphere: shallow planes plot as broad arcs near the edge, steep planes as tight arcs near the center, and a vertical plane becomes a straight line through the middle. Each plane also plots as a pole, the single red point representing the perpendicular to the plane, which is where serious analysis happens. Poles turn a tangle of arcs into a scatter of points, and clusters of points reveal the sets your eye could never separate from the great circles alone.
The density shading counts how many poles fall within a cone around every direction on the net and shades the result, so a genuine set shows as a dark bullseye and random scatter shows as flat grey. The counting cone controls the smoothing: a small cone near 8 degrees resolves tight sets and looks noisy on small datasets, while a wider cone near 20 degrees smooths a large dataset into broad maxima. Change it and watch which features survive, because features that vanish with slightly different smoothing were never real.
The numbers below the net
The mean pole is the average orientation of all your measurements, and the mean plane is that pole converted back into a strike and dip you can quote. The orange circle marks the mean pole and the orange arc is the mean plane. Vector strength R measures how tightly the data cluster: values above about 0.95 mean a well defined single set, values near 0.6 or lower usually mean you have mixed two sets together and should split the data before averaging. Averaging across two different joint sets produces a mean plane that describes nothing that exists in the rock, which is the most common way stereonet analysis goes wrong.
The rose diagram
The rose plots strike directions in five degree bins, mirrored across the center because a strike of 040 and 220 describe the same line. It answers a different question from the net: not how the planes are oriented in three dimensions, but which map directions dominate, which is what you want for lineament studies, joint spacing surveys, and comparing structures to a regional trend.
A worked example
Press the demo button and twenty measurements appear: ten bedding planes near 090/45, seven steep joints near 172/80, and three shallow readings near 008/35. The net immediately shows three clusters, the density shading picks out the two strong ones, and the rose shows the two dominant strike directions at roughly east west and north northwest. Try turning the great circles off to see how much clearer poles alone become, then widen the counting cone and watch the weakest cluster fade into the background where it belongs.
Stereonet Summary
| Planes | " + DATA.planes.length + " |
| Lines | " + DATA.lines.length + " |
| Mean orientation | trend " + MEAN.trend.toFixed(1) + ", plunge " + MEAN.plunge.toFixed(1) + " |
| Mean vector strength | " + (MEAN.strength*100).toFixed(1) + "% of " + MEAN.n + " observations |
| Projection | Schmidt equal-area, lower hemisphere, right hand rule |
Generated by calculatgeek.com Free Online Stereonet
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Type or paste structural measurements, planes as strike and dip, lines as trend and plunge, and the tool above plots them on a Schmidt equal-area lower hemisphere net exactly as a structural geologist would on the classic paper version. Planes appear as great circles with their poles marked, lineations plot as points, a rose diagram summarizes the strike population, and the mean orientation with its vector strength is computed automatically. The Load Demo button drops in two conjugate joint sets and a lineation so you can see a realistic dataset immediately.
This is the seventh tool in the Geoscience Workbench, and the field geology entry in a suite that otherwise lives in the subsurface. It uses the right hand rule convention throughout: dip direction is 90 degrees clockwise from the strike you enter.
Why geologists plot on a sphere
Orientations in three dimensions are hard to compare as numbers and easy to compare as points on a sphere. The stereonet projects the lower half of that sphere onto a circle, and the equal-area (Schmidt) version used here preserves relative areas, which is what makes point densities meaningful: a cluster of poles on a Schmidt net is a genuine orientation family, not a projection artifact. Two joint sets that look like thirty confusing field measurements in a notebook resolve into two tight great-circle bundles the moment they plot, and the angle between the conjugate sets even carries information about the stress field that made them.
Related Calculators and Reference
- Dip and Strike Three-Point Calculator for deriving orientation from three outcrop points.
- Geology Hardness Scale Tool for the mineral identification side of fieldwork.
- Mohr-Coulomb Calculator for the stress mechanics behind conjugate fracture sets.
- Free Online LAS File Viewer and the rest of the Geoscience Workbench in the bar above.
- External reference: Rick Allmendinger Stereonet, the standard desktop program this tool complements.