Fathom to Metre Converter

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Quick Conversions

Select a common maritime depth value for instant conversion between fathoms and metres.

Conversion Tables

Common Fathom to Metre Conversions

Fathoms (fath)	Metres (m)	Maritime Context
1	1.8288	Shallow coastal water
5	9.144	Typical harbour depth
10	18.288	Anchorage depth
20	36.576	Deep anchorage
50	91.44	Offshore depth
100	182.88	Continental shelf
200	365.76	Deep water navigation
500	914.4	Ocean depth
1000	1828.8	Abyssal zone

Metre to Fathom Reference

Metres (m)	Fathoms (fath)	Description
1	0.5468	Basic metric unit
5	2.7340	Swimming pool depth
10	5.4681	Recreational diving
20	10.9361	Advanced diving
50	27.3403	Professional diving
100	54.6807	Technical diving limit
200	109.3613	Submarine operations

Conversion Formulae

Fathoms to Metres

Formula: Metres = Fathoms × 1.8288

Example: Convert 25 fathoms to metres

25 fath × 1.8288 = 45.72 m

Metres to Fathoms

Formula: Fathoms = Metres × 0.546806649

Example: Convert 50 metres to fathoms

50 m × 0.546806649 = 27.34 fath

Step-by-Step Conversion

Converting Fathoms to Metres

1 Identify the value: Determine the number of fathoms you need to convert.

2 Apply the conversion factor: Multiply your fathom value by 1.8288 (the exact conversion factor).

3 Perform the multiplication: For instance, 15 fathoms × 1.8288 = 27.432 metres.

4 Round as needed: Round your result to the appropriate number of decimal places based on the required precision.

Converting Metres to Fathoms

1 Start with metres: Note the metre value you wish to convert.

2 Apply the conversion factor: Multiply by 0.546806649 or divide by 1.8288.

3 Complete the maths: For example, 30 metres ÷ 1.8288 = 16.404 fathoms.

4 Verify accuracy: Double-check your result and round to the desired precision.

Visual Depth Comparisons

Olympic Swimming Pool

2 metres

Approximately 1.09 fathoms deep

Recreational Diving Limit

40 metres

Approximately 21.87 fathoms depth

Submarine Periscope Depth

15 metres

Approximately 8.20 fathoms below surface

Average English Channel

63 metres

Approximately 34.45 fathoms at deepest

About Fathoms and Metres

What is a Fathom?

A fathom is a traditional nautical unit of depth measurement equal to six feet or 1.8288 metres. The term originates from the Old English word “fæðm,” meaning “outstretched arms.” Historically, sailors determined this measurement by extending their arms from fingertip to fingertip, which approximated six feet for an average person. Fathoms remain widely used in maritime navigation, depth sounding, and nautical charts, particularly in English-speaking seafaring nations.

What is a Metre?

The metre (British spelling) or meter (American spelling) is the fundamental unit of length in the International System of Units (SI). Originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole, the metre is now defined by the distance light travels in a vacuum during a specific fraction of a second. Metres are universally recognised in scientific, commercial, and everyday measurements across most of the world, including depth measurements in modern maritime applications.

Maritime History and Context

The fathom has ancient origins in seafaring traditions. Before the advent of electronic depth sounders, sailors measured water depth by lowering a lead line—a rope marked at fathom intervals with a lead weight attached. This method, known as “sounding,” allowed mariners to determine safe passages, locate anchorages, and avoid running aground. The practice of measuring depth in fathoms dates back centuries and was standardised across British and American navies.

Whilst modern vessels primarily rely on echo sounders and sonar technology, many nautical charts still reference depths in fathoms, particularly in regions with strong maritime traditions. The conversion between fathoms and metres has become essential as international shipping increasingly adopts metric measurements. Navigators, marine engineers, and oceanographers must be proficient in converting between these units to interpret charts accurately and maintain safe navigation practices.

Common Maritime Depths

Maritime Feature	Typical Depth (Fathoms)	Depth in Metres
Small boat harbour	2-5 fathoms	3.66-9.14 m
Marina berth	3-6 fathoms	5.49-10.97 m
Deep water port	10-20 fathoms	18.29-36.58 m
Anchorage zone	8-15 fathoms	14.63-27.43 m
Continental shelf edge	100-110 fathoms	182.88-201.17 m
Average ocean depth	2,000 fathoms	3,657.6 m
Mariana Trench (deepest)	6,000+ fathoms	10,972.8+ m

Frequently Asked Questions

How many metres are in one fathom?

One fathom equals exactly 1.8288 metres. This conversion factor is based on the definition of a fathom as six international feet, with each foot equalling 0.3048 metres. Therefore, 6 feet × 0.3048 = 1.8288 metres per fathom.

Why do sailors still use fathoms instead of metres?

Many nautical charts, particularly older ones or those used in regions with strong British or American maritime heritage, display depths in fathoms. The tradition persists due to historical precedent, the continued use of imperial measurements in some countries, and the fact that converting existing charts and training materials requires significant investment. However, international maritime regulations increasingly favour metric units.

What is the origin of the word “fathom”?

The word “fathom” derives from Old English “fæðm,” which meant “embrace” or “outstretched arms.” The measurement originally represented the distance between a person’s fingertips when both arms were extended horizontally, typically approximating six feet. This practical body-based measurement made it convenient for sailors to estimate rope lengths and water depths before standardised measuring instruments existed.

Are fathoms used for anything other than water depth?

Whilst fathoms are predominantly associated with measuring water depth in maritime contexts, they have also been used historically to measure the length of anchor chains, fishing lines, and rope. In modern usage, the term “fathom” has taken on a metaphorical meaning—”to fathom” something means to comprehend its depth or complexity. However, the literal measurement unit is now almost exclusively applied to nautical depth sounding.

How do I convert fathoms to feet?

Converting fathoms to feet is straightforward: simply multiply the number of fathoms by 6, since one fathom equals exactly six feet. For example, 10 fathoms × 6 = 60 feet. This conversion is more commonly used in countries that employ imperial measurements, whilst metric countries prefer fathom-to-metre conversions.

What depth is considered “deep water” in nautical terms?

In maritime navigation, “deep water” typically refers to depths exceeding 100 fathoms (approximately 183 metres), where the seabed has minimal influence on vessel navigation and wave behaviour. Depths between 10-100 fathoms (18-183 metres) are often classified as intermediate depths, whilst anything shallower than 10 fathoms (18 metres) requires careful navigation and is considered shallow water where grounding risks increase.

Do modern ships still measure depth in fathoms?

Modern vessels typically use electronic depth sounders and sonar systems that can display measurements in either fathoms or metres, depending on crew preference and the charts being used. International shipping standards increasingly favour metric units, but many experienced mariners, particularly in the UK and USA, remain comfortable with fathoms. Most contemporary navigation systems allow users to toggle between measurement units for convenience.

Is a fathom the same in all countries?

The international fathom is standardised at exactly 1.8288 metres or six international feet. However, historical variations existed before standardisation. For instance, the old British Admiralty used slightly different measurements in earlier centuries. Today, the international definition is universally accepted in maritime contexts, though some historical charts may reference older, slightly different fathom values.

Conversion Accuracy Tips

When converting between fathoms and metres, precision matters in maritime navigation. Here are key considerations for accurate conversions:

Exact conversion factor: Always use 1.8288 as the precise multiplier for fathoms to metres. Rounding this factor can introduce errors in critical navigation scenarios.
Decimal precision: For routine navigation, two decimal places suffice. However, hydrographic surveys and scientific research may require four to six decimal places.
Chart specifications: Always verify whether your nautical chart displays depths in fathoms, metres, or feet. This information typically appears in the chart legend or title block.
Tide corrections: Remember that charted depths usually represent values at a specific tide level (often mean lower low water). Apply appropriate tide corrections to your depth readings.
Safety margins: When planning passages in shallow water, always include a safety margin. Convert your vessel’s draught to the same units as your depth measurements and add clearance for waves, squat effect, and tidal variations.