Convert Length from Us Survey Foot to Nautical Mile (ft-us to nMi)

US Survey Foot to Nautical Mile Conversion Formula

To convert from US Survey Foot (ft-us) to Nautical Mile (nMi), use the following formula:

Example

Let's convert 5 US Survey Foot (ft-us) to Nautical Mile (nMi).

Using the formula:

Therefore, 5 US Survey Foot (ft-us) is equal to $0.00082289520285971968955$ Nautical Mile (nMi).

What is a US Survey Foot (ft-us)?

The US Survey Foot is a unit of length historically used for land surveying in the United States.

It is very close in length to the international foot, equaling approximately 1.000002 international feet (ft). The plural form is US Survey Feet.

Where Did the US Survey Foot Come From?

The origin of the US Survey Foot dates back to the Mendenhall Order of 1893. This order defined the relationship between the meter and US customary units.

It established that 1 meter is precisely equal to 39.37 inches. From this relationship, the US Survey Foot was derived, defined as 1200/3937 meters.

This definition differs slightly from the international foot, which was established in 1959 and is defined as exactly 0.3048 meters.

Why Was the US Survey Foot Replaced?

To simplify measurements and prevent confusion, the National Institute of Standards and Technology (NIST) and the National Geodetic Survey (NGS) made a critical change.

They officially retired the U.S. Survey Foot on December 31, 2022.

Surveying and mapping applications in the United States will now use the international foot. This critical change helps unify the National Spatial Reference System (NSRS) and prevents costly errors in large-scale projects.

Why Did This Small Difference Cause Big Problems?

While the difference between a US Survey Foot and an international foot is minuscule—only about two parts per million—it becomes significant over large distances.

For every mile, the discrepancy adds up to approximately 1/8 inch.

This minor error may not be significant for a backyard fence. However, for massive construction projects and infrastructure development, such as bridges that cross state lines, the accumulated error can lead to severe misalignments and costly mistakes.

What is a Nautical Mile (nmi)?

A nautical mile (nmi) is a unit of measurement used for sea and air travel, equal to 6,076 feet or 1,852 meters.

Quick Facts:

• 1 Nautical Mile = 1.15 statute miles (6,076 feet or 1,852 meters).
• It is based on the Earth's circumference (longitude and latitude).
• It is the standard unit of measurement for sea and air navigation.
• Speed for sea and air travel is measured in knots (one nautical mile per hour).

Why is a Nautical Mile Based on the Earth's Circumference?

A nautical mile is based directly on the size and shape of the Earth.

It is defined as one minute of arc along a meridian (a line of longitude).

Imagine the Earth as a circle of 360 degrees. Each of those degrees is divided into 60 smaller parts called "minutes."

One nautical mile is equal to one of these minutes of latitude.

This direct link to the planet's geometry makes the nautical mile essential for navigators, as it simplifies calculations on maps and charts.

What's the Difference Between a Nautical Mile and a Statute Mile?

While they both measure distance, nautical miles and statute miles (used on land) are not the same.

The key difference lies in how they are calculated and used.

• Statute Mile: This is the mile you know from road signs, equal to 5,280 feet. It's a fixed distance that doesn't take into account the Earth's curvature.

• Nautical Mile: This is a longer measurement, approximately 1.15 statute miles (6,076 feet). It is based on the Earth's curvature, aligning with the degrees of latitude and longitude used on navigational charts.

Using statute miles for long-distance sea or air travel would lead to significant errors, which is why navigators exclusively use nautical miles to ensure accuracy.

What is a Knot and How Does it Relate to Speed?

In maritime and aviation, speed isn't measured in miles per hour—it's measured in knots.

A knot is a unit of speed, not distance.

It is defined simply as one nautical mile per hour. This makes calculations very straightforward: a ship traveling at a steady 15 knots will cover 15 nautical miles in precisely one hour.

The term comes from the old sailors' practice of using a rope with knots tied at regular intervals, thrown overboard, to measure a ship's speed.

What is the imperial system?

US Survey Foot to Nautical Mile Conversion Table

Here are some quick reference conversions from US Survey Foot (ft-us) to Nautical Mile (nMi):