Altitude Meter.

Frequently asked questions.

How accurate is GPS altitude?

GPS altitude accuracy is typically ±10–30 metres under open sky, and occasionally worse in urban canyons or under dense tree cover. This is significantly less accurate than horizontal GPS position (which is usually 3–5 metres) because of the geometry of the satellite constellation — all GPS satellites are above you, which is great for pinpointing your latitude and longitude but less effective at resolving your vertical position. Our tool cross-references your GPS reading with the Copernicus Digital Elevation Model (a 90-metre resolution terrain database) to give a more reliable ground-level elevation figure. The raw GPS altitude and the database elevation will often differ by 5–20 metres — both are shown so you can compare.

Why does air pressure decrease at altitude?

Atmospheric pressure is simply the weight of all the air above you pressing down. At sea level, you have the full weight of the entire atmosphere above — approximately 10,000 kg per square metre — producing a pressure of about 1013 hPa. As you ascend, there is less air above you, so the pressure drops. The relationship is roughly exponential: near sea level, pressure falls by about 12 hPa per 100 metres of ascent. By the time you reach 5,500 metres (about the altitude of Everest Base Camp), pressure is roughly half of sea-level pressure. At the summit of Everest (8,849 m), pressure is less than a third of sea level. This reduction in pressure is why supplemental oxygen is needed at extreme altitudes — there are fewer oxygen molecules in each breath.

Why does water boil at lower temperatures at altitude?

Water boils when its vapour pressure — the pressure exerted by water molecules trying to escape into the air — equals the surrounding atmospheric pressure. At sea level (1013 hPa), that equilibrium happens at 100°C (212°F). At altitude where atmospheric pressure is lower, less energy (heat) is needed to reach that equilibrium, so the boiling point drops. At 1,000 m elevation, water boils at roughly 96°C. At 3,000 m it boils around 90°C, and at 5,000 m around 83°C. This has real consequences for cooking: pasta, eggs, rice, and vegetables all need longer cooking times at altitude because the boiling water is cooler. Many high-altitude recipe adjustments account for this — adding several minutes of cooking time per 1,000 metres of elevation.

What is altitude vs elevation?

In precise usage, elevation refers to vertical distance above sea level measured at a point on the ground — it describes the terrain. Altitude usually refers to the vertical distance of an object above some reference, often the ground directly below it (e.g., an aircraft flying at 10,000 feet altitude). In everyday speech — and on this tool — the two terms are used interchangeably to mean your height above mean sea level (MSL). Mean sea level itself is defined as the average ocean surface level, smoothed over time to remove tidal variation, and serves as the global reference datum for elevation worldwide.

Understanding Altitude and Elevation

Altitude is simply how high you are above a reference point — in most cases, mean sea level (MSL). This tool reads your GPS position and looks up your elevation from the Copernicus Digital Elevation Model, a high-resolution terrain dataset that covers the entire globe. The result is displayed in both metres and feet so you can use whichever unit feels natural.

How GPS altitude works — and why it's less precise than you'd expect

GPS satellites orbit in a near-circular band roughly 20,000 km above Earth. Because all the satellites are above you and spread across a relatively narrow band of sky, the geometry is good for pinpointing your horizontal position (latitude and longitude) but less ideal for vertical position (altitude). The typical horizontal GPS accuracy on a modern smartphone is 3–5 metres; vertical accuracy is usually 10–30 metres. Our tool supplements the raw GPS reading with a terrain elevation database to improve accuracy on the ground.

Air pressure at altitude

The atmosphere is thickest at sea level where the entire column of air above is pressing down on you. As you climb, there is less air above, so atmospheric pressure drops. Near sea level, pressure falls by roughly 12 hPa for every 100 metres of ascent. The tool calculates this using the International Standard Atmosphere (ISA) model, which assumes a standard temperature lapse rate of 6.5°C per 1,000 metres. The actual pressure on any given day will vary slightly due to weather, but the ISA figure is a reliable baseline for planning purposes.

Why does this matter? Pilots, mountaineers, and weather observers use pressure altitude constantly. Many altimeters on aircraft and watches are actually barometers that infer altitude from air pressure — the reverse of what we're doing here. If you're carrying a barometric altimeter watch, you can cross-check its reading against the GPS elevation shown here.

Why water boils at a lower temperature at altitude

Water boils when its vapour pressure equals the surrounding atmospheric pressure. At sea level, that happens at 100°C (212°F). At 3,000 metres, where atmospheric pressure is roughly 70 kPa instead of 101 kPa, water boils at around 90°C (194°F). This has real-world consequences: food takes longer to cook in boiling water at altitude because the water is cooler, pasta and eggs need extra time, and camping coffee may taste flat because the water never gets hot enough to extract flavour properly. The boiling point shown by this tool is calculated directly from the estimated air pressure.

Terrain categories

The tool classifies your current elevation into a broad terrain category — sea level, lowland, hills, mountains, high alpine, or extreme altitude — to give an intuitive sense of where you are in relation to typical landscapes. These thresholds follow general geographic conventions: below 200 m is lowland, 200–600 m is hills, 600–1,500 m is mountains, 1,500–3,500 m is high alpine, and above 3,500 m is extreme altitude. The extreme category is particularly important for safety: at these heights, reduced oxygen and lower boiling points can both have significant physical effects.

Practical uses for an altitude meter

Hikers and mountaineers use elevation data to pace climbs, estimate remaining ascent to a summit, and monitor acclimatisation. Trail runners and cyclists use it to plan effort on hilly routes. Travellers arriving at high-altitude destinations like Cusco, Kathmandu, or La Paz can check their altitude immediately on landing to understand why they might feel breathless. Campers and outdoor cooks can quickly check the boiling point before starting a meal. Drone operators and paragliders often need their above-sea-level elevation to comply with airspace rules.