Online compass

North is where the N on the compass rose points once the compass is running, and the large figure says how far the phone is turned from it. A magnetometer in the phone measures the direction of the Earth's magnetic field. An accelerometer and a gyroscope track how the phone is tilted and turned. The phone combines the three into one orientation, which the page turns into a heading from 0 to 359 degrees, counted clockwise.

The heading is the direction the phone points. Lying flat, that is the way the top edge faces. Held upright like a camera, it is the way the back of the phone faces, and any angle in between works, in portrait or landscape. The rose turns with the phone, while a fixed red mark at the top shows where it is aimed.

Next to the figure the reading names one of 16 compass points, each covering 22.5° of the circle. The four cardinal points are north, east, south and west, at 0°, 90°, 180° and 270°. Halfway between them sit north-east, south-east, south-west and north-west, and the eight points in the gaps take three letters. A heading of 200° reads as SSW, south-south-west.

Nothing has to be installed: this is a compass without app, account or download, and one tap on Start the compass sets it going. Asked "where is the compass on my phone?", the answer here is the browser itself. On an iPhone or iPad, Safari then asks once for access to motion and orientation, and that request has to come from the tap.

Safari reports a magnetic compass heading of its own, along with an accuracy figure that the page shows. Chrome and Firefox on Android hand the page the phone's orientation referenced to the Earth directly. The W3C DeviceOrientation Event Specification calls that kind of reading absolute, and makes it available only to pages served over a secure HTTPS connection.

Most laptops and desktop computers have no magnetometer. When no reading arrives within 1.5 s of the start, the page says so and offers the Declination view instead, which works on any computer. A refused permission gets a notice of its own.

While the compass runs, the page asks the browser to keep the screen awake through the Screen Wake Lock, where that is offered. The display then does not dim halfway through a reading, and Stop ends the reading and lets the screen sleep again.

Ordnance Survey's guide "A tale of three norths" separates the three directions a walker meets. True north runs along a meridian to the geographic North Pole. Magnetic north is where a compass needle settles, pulled by the planet's field. Grid north is, in the guide's words, "the north to which the grid lines on your map points".

Magnetic declination is the angle from the first of these to the second, measured east or west. The OS guide writes it as "Magnetic Variation (Declination)", so magnetic variation is the same angle under another name. Some hillwalking books use magnetic variation for the angle from grid north instead. That is a different figure, and many mix-ups between map and compass begin there.

Where the declination is zero the needle points along the meridian, and the line joining such places is the agonic line. The British Geological Survey (BGS) reported that compasses at Greenwich pointed to true north in September 2019, for the first time since around 1660. It put the agonic line's drift at around 20 km a year westwards, and expected every compass in the UK to point east of it by 2040.

The North reference switch chooses which north the dial reads from. The magnetic setting shows what the sensor measures. The true setting adds the declination of the place picked in the Declination view, London until another is chosen. The date is that view's too, today unless it is changed, and a line under the switch names the place, the date and the angle in use.

On 1 January 2026 the declination at the 12 listed places ran from 1.4° west at Belfast to 1.5° east at Norwich. Every one of them drifts eastwards each year, by between 0.17° and 0.21°.

Magnetic north lies within 2° of true north anywhere in the United Kingdom. On 1 January 2026 the World Magnetic Model 2025 (WMM2025) put the needle 1.1° east of the meridian in London, 1.5° east in Norwich and 1.4° west in Belfast. Scotland, Northern Ireland and the far south-west of England sat on the western side. Most of England and Wales, from Newcastle upon Tyne down to London and Cardiff, sat on the eastern side.

Everywhere the angle grows eastwards by about 0.17° to 0.21° a year, so western places move towards zero and eastern ones away from it. A bearing therefore needs the local figure for its date, not one national number. The compass adds that figure to the magnetic heading when the true setting is chosen. The declination panel gives it for any UK place and any day up to 31 December 2029.

The agonic line is crossing Britain meanwhile. The model puts Manchester through zero in January 2025, Cardiff in September 2025, Plymouth in December 2026 and Edinburgh in May 2028. On 1 January 2026, Plymouth, Edinburgh, Glasgow, Inverness and Belfast still lay on the western side.

WMM2025 is produced by NOAA's National Centers for Environmental Information (NCEI) with the BGS. NOAA released it on 17 December 2024 and gives 31 December 2029 as its last valid day, after which WMM2030 takes over. It describes the main field with 168 coefficients up to degree 12, and every figure the panel shows is worked out from them in the browser.

NCEI's error model gives the uncertainty of the declination, one standard deviation, in degrees. It is the square root of 0.26 squared plus (5,417 ÷ H) squared, where H is the horizontal field in nanotesla. In London H is 19.5 µT, which gives ±0.38°. The model leaves out magnetised rock in the crust, and NCEI notes that local, regional and temporal anomalies can exceed 10°.

The declination panel also gives the inclination, or dip, of the field below the horizontal (66.5° in London) and its total strength (49.1 µT). The checked cases compare its results with the BGS WMM2025 calculator for London and Belfast, and with one of NOAA's published test values.

OS calls the angle between grid north and magnetic north its Grid Magnetic Angle (GMA). It is the figure that links a direction taken from an OS map to a compass. On 1 January 2026 the model had the needle 0.39° west of grid north in London and 0.97° east of it in Cardiff.

OS prints the angle on its paper maps. Landranger maps show it as a diagram in the middle of the north margin and again in the legend, while Explorer maps give the detail in the legend. The printed figure, OS adds, is correct only at the time of printing. The magnetic data on its maps come from the BGS.

The OS memory aid, "from grid to mag add, from mag to grid get rid", was written for a needle pointing west of the grid lines. London still had that case on 1 January 2026: 90° measured on the map becomes 90.4° on the compass. OS also notes that magnetic north has moved east of grid north for the first time since the 1660s, starting in the south-west.

Where the needle lies east of the grid lines, the arithmetic reverses: the GMA comes off going from map to compass and goes back on the other way. At Cardiff, 90° read off the map turns into 89.0° on the compass. Under Map and compass bearings, the declination panel says which way round applies at the chosen place and date. It then turns a map bearing into the compass setting and the true bearing.

The BGS Grid Magnetic Angle Calculator, which runs the survey's own regional model of the UK, gives the angles below for July 2026. This page's results for the same month come from the global model and differ from them by less than 7′.

Great Britain's maps use the National Grid. The OS coordinate guide defines it as a Transverse Mercator projection on the Airy 1830 ellipsoid, with its true origin at 49° N, 2° W. Grid lines and meridians run parallel only along that central meridian. East of it, as in London, grid north lies 1.47° east of the meridian.

Northern Ireland's maps use the Irish Grid, with its origin at 53° 30′ N, 8° W, and the declination panel switches to it for Belfast. There the needle lay 3.05° west of the Irish Grid's north on 1 January 2026, so a map reading of 90° needs 93.0° on the compass.

A bearing is a direction in degrees clockwise from north, and the Bearing to follow box keeps one in view. Typing a figure from 0 to 359, or tapping Use current heading, fixes it and marks it on the rose. The page then says "Turn right" or "Turn left" with the degrees still to go, and "On course" once the phone points less than 3° away from it.

The bearing is read against whichever north the switch shows. With the magnetic setting it matches a baseplate compass; with the true setting it is a true bearing, measured from the meridian. In London on 1 January 2026 a magnetic 90° was a true 91°. A bearing taken off an OS map is a grid bearing, and the converter in the declination panel turns it into either of the others.

Hold reading freezes the figure on screen until Release is tapped, so a direction can still be read after the phone is lowered or turned away. The Needle setting decides how quickly the dial follows the sensor. Quick reacts at once but trembles more, Calm smooths the movement but lags behind a fast turn, and Balanced sits between them.

Every setting goes into the page address: view, place or typed coordinates, a changed date, height, map grid, north reference, bearing and needle. A copied link therefore reopens the same view on another phone. A position found with My position is never written into it, and nothing is stored in the browser.

A garden faces the direction someone looks when standing at the back of the house and facing down the garden, and the phone's heading gives it directly. The phone can lie flat with its top edge pointing away from the house, or stand upright with its back to the garden. Either way it shows that direction in degrees and as a compass point.

A south-facing garden reads S at headings close to 180°, with SSE and SSW either side, while a north-facing one reads close to 0°. In the northern hemisphere the Sun stands due south at local noon. A south-facing garden therefore looks towards the midday Sun, while a north-facing one has the house between it and the Sun.

For a garden aspect the choice of north hardly matters. Across the UK the needle and the meridian differed by at most 1.5° on 1 January 2026, far less than the 22.5° one compass point covers. Steel in walls, radiators and kitchen appliances can disturb a magnetometer, so a reading out on the lawn, away from the back wall, is less exposed to it.

The aspect also decides how a boundary hedge shades the ground: a tall hedge on the south side of a garden throws its shadow across it. The high hedge checker uses the direction in which a hedge lies from a garden to work out the height at which it starts to take a neighbour's light.

A phone compass drifts when its magnetometer has lost its calibration or when something magnetic is close by. Google's Maps help for Android describes calibration as moving the phone in a figure of eight until the beam on the map narrows. Apple's iPhone guide asks for the phone to be held flat with the crosshairs lined up, and says magnetic or environmental interference can affect accuracy.

The Calibrate the compass panel on the page sums both up: away from magnets, metal and other devices, then a few figures of eight. On an iPhone the page also shows the accuracy Safari reports, in degrees, and suggests calibrating when that figure goes above 20°. Android browsers give pages no accuracy figure, so there a calibration and a check against a known direction are the only tests.

Nothing here makes the sensor more exact than it is. The north switch adds the model's declination, uncertain by about 0.38° in London, but it cannot correct an error in the magnetometer itself. Measuring tools on a phone share that limit: the online ruler needs a card or a coin to set its scale before its centimetres are real.

Apple describes the iPhone's digital compass as help for basic navigation only. Scottish Mountain Rescue's safety advice is to carry a map and compass and know how to use them. It adds that smartphones and GPS "should not be relied on solely". A phone reading is a convenience in a street or a garden, not a replacement for those on the hill.