Face the Kaaba.

How this is calculated

The bearing is the initial heading of the great-circle route from your location to the Kaaba’s coordinates (21.4225°N, 39.8262°E), computed with the standard spherical-trigonometry formula. It is not simply “the direction of Mecca on a flat map” — for most of the world the great-circle bearing points noticeably north of that. The full derivation, the constants and a worked example are set out in how the qibla is calculated.

A flat (Mercator-style) map distorts distance and direction badly the further you get from the equator, so drawing a straight line from your city to Mecca on a paper map and reading its angle gives the wrong bearing almost everywhere outside the Arabian Peninsula. The correct qibla is the shortest path over the curved surface of the Earth — the same reason a flight from New York to Dubai arcs up near Greenland instead of heading straight east. From London, for example, the great-circle qibla points roughly south-east — not the due-south-east a flat map would suggest — because the shortest arc bends north before curving down toward the Arabian Peninsula. From New York it points north-east, not the south-east a flat map implies, for the same reason.

This is also the most common reason two qibla apps disagree by more than a degree or two: one is using the correct great-circle formula and the other a flat-map approximation, or the two are reading the phone's compass sensor differently. A phone compass measures magnetic north, which is offset from true north by a location-dependent amount called magnetic declination — a good app corrects for this automatically, but a bare compass app does not. If your result looks off, the most reliable check is to compare the bearing number itself (in degrees from true north) against a second calculator rather than trusting the needle alone, and to hold the phone flat and away from metal or magnets when reading a live compass.