Fathoms
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Equivalent depth
Accurate depth conversion between metres (m) and fathoms (ftm)
Convert metres to fathoms instantly with precise calculations. Includes reverse fathoms to metres conversion, feet, yards, nautical miles, and kilometres outputs, full formula reference, and depth conversion tables for 2026.
Professional depth conversion for nautical navigation, marine science, diving, hydrography, and ocean engineering
Convert metres to fathoms using the exact international definition: 1 fathom = 1.8288 metres, established precisely in 1959 by the international yard and pound agreement. This makes 1 metre = 0.546806649 fathoms (1 ÷ 1.8288). Our tool delivers precise results across six depth and length units simultaneously — fathoms, feet, yards, metres, kilometres, and nautical miles — giving you a complete multi-unit breakdown from a single input value with no rounding errors, essential for nautical charting, diving, and marine surveying in 2026.
Switch seamlessly between metres to fathoms and fathoms to metres conversion modes. Whether you are reading a nautical chart with depth marked in fathoms and need the metric equivalent for modern navigation equipment, converting a dive profile depth from metres to fathoms for a traditional log entry, translating a hydrographic survey result, or checking anchor chain scope in both units, both directions are covered instantly from a single input value without manual calculation in 2026.
Essential for maritime navigation and nautical charting, SCUBA and recreational diving, commercial fishing and trawling, oceanography and hydrographic surveying, marine engineering and offshore construction, anchor and mooring calculations, submarine cable and pipeline laying, and any field where water depth or vertical marine distances must be communicated across metric and imperial unit systems. Many nautical charts published before the 1980s use fathoms, making this converter indispensable for interpreting legacy data in 2026.
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The metre (m) is the SI base unit of length, defined as the distance light travels in vacuum in exactly 1/299,792,458 of a second. The fathom (ftm) is a traditional unit of depth used in maritime and nautical contexts, defined as exactly 6 feet, which since the 1959 international agreement equals exactly 1.8288 metres. The fathom originated from the Old English "fæthm," meaning "outstretched arms" — the approximate span of a sailor's arms from fingertip to fingertip, which was used to measure rope and anchor chain lengths by hand aboard ships before standardised measurement was universal. Converting between metres and fathoms uses the factor: 1 m = 0.546806649... fathoms (= 1 ÷ 1.8288).
While the fathom has been largely superseded by the metre in modern hydrography and navigation, it remains in active use on older nautical charts, in traditional seamanship, in the commercial fishing industry (particularly in the UK and US), and in recreational diving publications. Many British Admiralty charts published before metrication in the 1960s–1970s mark depths in fathoms and feet, and some US nautical charts still use fathoms for shallow-water soundings. The origin of the phrase "to fathom something" — meaning to understand its depth — comes directly from this unit's historical use in sounding ocean depths with a lead line. See NIST for official unit definitions at nist.gov.
1 fathom = 6 feet = 2 yards = 1.8288 metres (exact, by international definition since 1959). The fathom was traditionally used for measuring sea depth by dropping a lead-weighted line over the side of a vessel and counting the number of arm-spans pulled up.
The table below covers the most commonly needed metre values for fathom conversion in nautical navigation, marine diving, fishing, and hydrographic surveying in 2026. For related length conversions, see our Miles to Kilometres Converter.
| Metres (m) | Fathoms (ftm) | Feet (ft) | Yards (yd) | Common Reference |
|---|---|---|---|---|
| 0.9144 m | 0.5 ftm | 3 ft | 1 yd | Half fathom |
| 1.8288 m | 1 ftm | 6 ft | 2 yd | 1 fathom exactly |
| 3.6576 m | 2 ftm | 12 ft | 4 yd | Shallow harbour sounding |
| 5.4864 m | 3 ftm | 18 ft | 6 yd | Coastal passage depth |
| 9.144 m | 5 ftm | 30 ft | 10 yd | Common anchorage depth |
| 10 m | 5.468 ftm | 32.81 ft | 10.94 yd | Recreational dive limit (beginner) |
| 18.288 m | 10 ftm | 60 ft | 20 yd | Coastal shelf sounding |
| 20 m | 10.936 ftm | 65.62 ft | 21.87 yd | PADI Open Water max depth |
| 30 m | 16.404 ftm | 98.43 ft | 32.81 yd | Advanced Open Water max depth |
| 36.576 m | 20 ftm | 120 ft | 40 yd | Common chart depth contour |
| 40 m | 21.872 ftm | 131.23 ft | 43.74 yd | Technical dive limit (Divemaster) |
| 91.44 m | 50 ftm | 300 ft | 100 yd | Continental shelf edge reference |
| 100 m | 54.681 ftm | 328.08 ft | 109.36 yd | 100-metre depth — key reference |
| 182.88 m | 100 ftm | 600 ft | 200 yd | 100 fathoms — deep chart line |
| 200 m | 109.361 ftm | 656.17 ft | 218.72 yd | Edge of continental shelf (~200 m) |
| 1,000 m | 546.807 ftm | 3,280.84 ft | 1,093.61 yd | 1 km depth — deep sea start |
| 1,828.8 m | 1,000 ftm | 6,000 ft | 2,000 yd | 1,000 fathoms exactly |
| 10,000 m | 5,468.07 ftm | 32,808 ft | 10,936 yd | Near deepest ocean trench |
Use this reverse table when reading a nautical chart, dive guide, or fisheries report in fathoms and needing to convert to metres for modern navigation instruments, GPS systems, or metric scientific analysis.
| Fathoms (ftm) | Metres (m) | Feet (ft) | Nautical Miles | Common Reference |
|---|---|---|---|---|
| 0.5 ftm | 0.9144 m | 3 ft | 0.000494 nmi | Half fathom — shallow bar |
| 1 ftm | 1.8288 m | 6 ft | 0.000988 nmi | 1 fathom exactly |
| 2 ftm | 3.6576 m | 12 ft | 0.001976 nmi | Shallow anchorage |
| 3 ftm | 5.4864 m | 18 ft | 0.002964 nmi | Coastal harbour depth |
| 5 ftm | 9.144 m | 30 ft | 0.004939 nmi | Typical anchorage |
| 10 ftm | 18.288 m | 60 ft | 0.009879 nmi | Coastal passage |
| 15 ftm | 27.432 m | 90 ft | 0.014819 nmi | Dive site reference |
| 20 ftm | 36.576 m | 120 ft | 0.019759 nmi | Deep anchorage |
| 30 ftm | 54.864 m | 180 ft | 0.029638 nmi | Offshore fishing ground |
| 50 ftm | 91.44 m | 300 ft | 0.049396 nmi | Continental shelf |
| 100 ftm | 182.88 m | 600 ft | 0.098793 nmi | 100 fathom line — chart contour |
| 200 ftm | 365.76 m | 1,200 ft | 0.197585 nmi | Deep shelf edge |
| 500 ftm | 914.4 m | 3,000 ft | 0.493963 nmi | Upper bathypelagic zone |
| 1,000 ftm | 1,828.8 m | 6,000 ft | 0.987927 nmi | Deep ocean — 1,000 fathom line |
| 3,000 ftm | 5,486.4 m | 18,000 ft | 2.963781 nmi | Abyssal zone reference |
The metre-to-fathom conversion bridges metric and traditional imperial systems in a range of marine, scientific, and recreational contexts.
British Admiralty charts, US NOAA charts, and many other international nautical charts produced before the 1970s–1980s metrication period mark water depth soundings in fathoms and fractions. Modern electronic chart display and information systems (ECDIS) use metres, creating a constant need to convert legacy fathom data. The 100-fathom line (182.88 m) is a classic bathymetric contour used to delineate the edge of the continental shelf on traditional charts, and mariners still reference it routinely when planning offshore passages in 2026.
Dive tables, dive computers, and certification agency materials frequently reference both metres and feet/fathoms for maximum operating depth. PADI Open Water Diver certification permits dives to 18 m (approximately 10 fathoms); Advanced Open Water permits 30 m (about 16.4 fathoms); and technical divers may work to 40 m (21.9 fathoms) or beyond. Divers consulting older American dive guides, US Navy dive tables, or historical wreck charts often encounter fathom measurements that must be converted to metres for modern dive computer programming and safety calculations in 2026.
The fishing industry in the UK, US, Canada, and Australia uses fathoms extensively for describing fishing grounds, net depths, trawl depths, and anchor line lengths. Longline fishing vessels set lines at specific depth targets often referenced in fathoms from traditional practice — a 50-fathom set equals 91.44 m. Deep-sea trawlers operating on the continental shelf at 100–200 fathoms (182–365 m) must reconcile traditional depth language with modern sonar and echo-sounder readouts in metres, requiring reliable fathom-to-metre conversion aboard commercial vessels in 2026.
Oceanographers studying bathymetry (the measurement of underwater topography) work across historic datasets that use fathoms alongside modern surveys conducted in metres. The deepest point of the ocean — the Challenger Deep in the Mariana Trench — is approximately 10,935 m deep (about 5,980 fathoms). Hydrographic surveys, sediment core location records, and tidal gauge data spanning the 19th and 20th centuries routinely use fathoms, and converting this legacy data to metres is essential for building comprehensive, continuous ocean depth databases and climate records in 2026.
Offshore oil and gas engineers, subsea pipeline designers, and submarine cable operators work with precise water depth measurements when selecting equipment rated for specific pressure depths. Riser systems, remotely operated vehicles (ROVs), drilling equipment, and repeater housings are rated at specific depth capacities often specified in both metres and fathoms. The deepest producing oil wells in 2026 operate at water depths exceeding 3,000 m (approximately 1,640 fathoms), and converting between these units is standard practice in offshore engineering documentation and regulatory submissions.
Proper anchoring technique requires paying out anchor chain equal to 5–7 times the water depth (the "scope ratio"). Sailors anchoring in 10 m (5.47 fathoms) of water should pay out 50–70 m (27–38 fathoms) of chain. Traditional anchor chain and rode is often marked in fathom increments (with coloured markers every 5 fathoms) even on modern vessels, while depth sounders read in metres. Converting between the two units is a regular, safety-critical task performed by offshore sailors, harbour masters, and mooring contractors every time a vessel anchors in 2026.
Since 1 fathom = 1.8288 m, a practical mental shortcut is to divide metres by 1.8 and subtract a small correction, or more precisely to multiply metres by 0.5468. Easier still: to convert metres to fathoms, divide by 2 and add about 9% — e.g., 100 m ÷ 2 = 50, × 1.09 ≈ 54.7 fathoms. For the reverse (fathoms to metres), multiply by 1.8 and add about 1.6% — e.g., 10 fathoms × 1.8 = 18, + 1.6% ≈ 18.29 m. The cleanest anchor: 10 fathoms = 18.288 m and 100 fathoms = 182.88 m — memorise these two and you can quickly estimate any conversion in your head at sea.
Converting metres to fathoms requires a single division by 1.8288. Here is the complete step-by-step process including all related length units.
Be aware that not all historical fathom definitions are identical. The international fathom of exactly 6 feet (1.8288 m) has been standard since 1959, but older British charts may use the Admiralty fathom of 6.00 feet (identical in this case), while some historical sources defined the fathom as 5.5 or 5.6 feet in specific regional traditions. When reading old nautical charts, always verify whether soundings are in fathoms, fathoms and feet (e.g., "5₃" meaning 5 fathoms 3 feet = 9.144 + 0.9144 = 10.058 m), or metres — modern ECDIS charts and post-1970s paper charts generally use metres. The US nautical mile was defined as 6,076.1 feet until 1954 (slightly different from the current international nautical mile of 1,852 m), which can affect fathom calculations on very old American charts.
The fathom is a unit of length equal to exactly 6 feet (1.8288 metres), used primarily in maritime and nautical contexts to express water depth. Its definition was standardised under the international yard and pound agreement of 1959, signed by the US, UK, Australia, Canada, New Zealand, and South Africa. Prior to metrication, nearly all international nautical charts used fathoms for depth soundings, and the unit remains in use on legacy charts, in traditional seamanship, fishing, and recreational diving in 2026. The word "fathom" also survives in general English as a verb meaning to understand the full depth of something.
NIST SI Reference →Reading nautical charts requires understanding depth sounding units. British Admiralty charts produced before approximately 1967 mark depths in fathoms; those produced between 1967 and the 1980s may show fathoms with feet subscripts (e.g., "5₃" = 5 fathoms 3 feet = 10.06 m); and modern charts use metres. The chart title panel specifies the unit used. Australian Hydrographic Service charts (AHS) and AMSA publications use metres exclusively. When navigating with a mix of old and new charts, always verify the unit before interpreting depth soundings to avoid serious navigation errors. Our metres-to-fathoms converter helps you cross-reference both systems instantly.
Miles to km →Whether converting depth between metres and fathoms, distance between miles and kilometres, length between mm and metres, mass between µg and mg, volume between mL and litres, speed between mph and km/h, or pressure between atmospheres and pascals, our complete library of free, bidirectional metric and imperial converters delivers instant, precise results with full multi-unit breakdowns for every conversion needed in marine science, navigation, engineering, medicine, and everyday life in 2026.
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