Free Online Phone Clinometer and Compass for Strike and Dip

Heading to the field? Install this site from your browser menu and this tool works with no signal. See how

Your phone already carries the instruments

A traditional compass clinometer does two jobs: it measures the direction a surface faces and how steeply it tilts. Your phone carries the same physics in miniature. An accelerometer senses which way gravity pulls, which gives tilt, and a magnetometer senses the magnetic field, which gives heading. Put together, a phone lying flat on a bedding plane or a joint surface can report dip, dip direction, and strike in a couple of seconds, with nothing to install and nothing leaving your browser.

How to take a reading

Press the enable button above and allow motion sensors if your phone asks. Lay the phone flat against the surface you want to measure, screen facing up, and give the numbers a moment to settle. The bubble display works like the level on a survey instrument: the dot drifts toward the downhill side of the phone. When the reading is steady, type a short note such as the outcrop name and press Record. Each reading lands in the table with strike written in the right hand rule convention, so the dip direction always sits ninety degrees clockwise from strike.

On a desktop computer there are no orientation sensors, so the manual entry boxes let you type the two tilt angles and a heading directly. That is also a handy way to check readings taken with a traditional instrument.

The mathematics behind the numbers

The phone reports two tilt angles, beta for rotation about its short axis and gamma for rotation about its long axis. The dip of the surface is the angle between the phone and a level plane, which works out to the arccosine of the product of the cosines of the two tilts. The downhill direction comes from projecting the gravity vector onto the face of the phone, and adding the compass heading turns that local direction into a true azimuth. Strike then follows from the right hand rule as the dip direction minus ninety degrees.

Accuracy and honest limits

Phone magnetometers are the weak link. They drift near steel, magnets, and electric currents, and many phone cases contain magnets that ruin headings entirely. Take the phone out of a magnetic case, keep it away from your hammer and belt buckle, and calibrate the compass with a figure of eight motion before a mapping session. Tilt readings from the accelerometer are far more dependable, usually within a degree or two of a good clinometer. Treat this as a fast reconnaissance instrument: excellent for collecting many readings quickly, not a replacement for a calibrated geological compass where a few degrees matter. Note that on some phones the heading is relative rather than true north, so check the heading readout against a known direction before trusting it.

From the field to a stereonet

The export button writes a CSV with strike, dip, dip direction, and your notes, in the plane convention that common stereonet programs accept. Collect readings across an outcrop, export the file, and plot poles to bedding or joint sets the moment you are back at a computer. Your readings never leave the phone: everything is computed and stored in the browser on the device in your hand.

Related Calculators and Reference

• Cross Section Maker: draw geological sections from borehole data.
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• Borehole Log Creator: build a clean borehole log from field descriptions.
• 3D Well Path and Borehole Viewer: rotate drillhole traces in three dimensions.
• Stereonet by Rick Allmendinger: the classic free program for plotting the CSV this tool exports.