Knots to MPH Converter - Nautical Speed Converter

What is a knot?

A knot is a unit of speed equal to one nautical mile per hour. It's the standard speed measurement for maritime and aviation navigation worldwide. The term comes from the historical practice of measuring ship speed by counting knots on a rope line.

Knots to mph conversion

The conversion formula

$$\text{mph} = \text{knots} \times 1.15078$$ $$\text{knots} = \text{mph} \times 0.868976$$

Why 1.15078?

One nautical mile equals 1.15078 statute miles. Since both measure distance per hour:

$$1 \text{ knot} = \frac{1 \text{ nautical mile}}{1 \text{ hour}} = \frac{1.15078 \text{ statute miles}}{1 \text{ hour}} = 1.15078 \text{ mph}$$

Common speed conversions

Knots to other units

Knots	MPH	KM/H	M/S
1	1.15	1.85	0.51
5	5.75	9.26	2.57
10	11.51	18.52	5.14
15	17.26	27.78	7.72
20	23.02	37.04	10.29
25	28.77	46.30	12.86
30	34.52	55.56	15.43
40	46.03	74.08	20.58
50	57.54	92.60	25.72

MPH to knots

MPH	Knots	KM/H
5	4.34	8.05
10	8.69	16.09
15	13.03	24.14
20	17.38	32.19
30	26.07	48.28
40	34.76	64.37
50	43.45	80.47
60	52.14	96.56
70	60.83	112.65

Why use knots?

Nautical miles make navigation easier

Nautical miles are based on Earth's geometry:

• 1 nautical mile = 1 minute of latitude
• 60 nautical miles = 1 degree of latitude
• This makes chart navigation intuitive

International standard

Knots are used universally in:

• Maritime shipping
• Commercial aviation
• Military operations
• Weather forecasting (wind speeds)
• Recreational boating

Wind speed scales

Beaufort scale

Force	Knots	MPH	Description
0	0-1	0-1	Calm
1	1-3	1-3	Light air
2	4-6	4-7	Light breeze
3	7-10	8-12	Gentle breeze
4	11-16	13-18	Moderate breeze
5	17-21	19-24	Fresh breeze
6	22-27	25-31	Strong breeze
7	28-33	32-38	Near gale
8	34-40	39-46	Gale
9	41-47	47-54	Strong gale
10	48-55	55-63	Storm
11	56-63	64-72	Violent storm
12	64+	73+	Hurricane

Hurricane categories

Category	Knots	MPH	Damage
1	64-82	74-95	Minimal
2	83-95	96-110	Moderate
3	96-112	111-129	Extensive
4	113-136	130-156	Extreme
5	137+	157+	Catastrophic

Speed in different contexts

Sailing speeds

Boat type	Typical speed (knots)
Dinghy	5-8
Cruising sailboat	5-8
Racing yacht	8-15
America's Cup	30-50
Foiling boats	40-60+

Ship speeds

Vessel type	Typical speed (knots)
Cargo ship	12-15
Container ship	20-25
Cruise ship	20-24
Ferry	15-25
Naval destroyer	30+
Aircraft carrier	30+

Aircraft speeds

Aircraft type	Typical speed (knots)
Small propeller	100-150
Commercial jet	450-550
Military fighter	500-1,200+

Note: Aircraft also use Mach numbers at high speeds.

Nautical mile vs. statute mile

Measurement	Value
Statute mile	5,280 feet
Nautical mile	6,076 feet
Ratio	1 nm = 1.151 sm

Why the difference matters

Using statute miles at sea would require complex calculations for navigation. Nautical miles align with latitude degrees, making position calculations straightforward.

History of the knot

Origin of the term

Sailors measured speed using a "chip log":

1. Wooden board attached to rope with knots
2. Knots spaced 47 feet 3 inches apart
3. Board thrown overboard
4. Count knots passing in 28 seconds
5. Number of knots = speed in knots

The spacing was calculated so knots corresponded directly to nautical miles per hour.

Modern measurement

Today, speed is measured by:

• GPS systems
• Doppler radar
• Pitot tubes (aircraft)
• Electronic logs

Aviation usage

Airspeed types

Type	Abbreviation	Description
Indicated	IAS	Read from airspeed indicator
Calibrated	CAS	IAS corrected for instrument error
True	TAS	CAS corrected for altitude/temperature
Ground	GS	Actual speed over ground

All measured in knots for international consistency.

Flight planning

Pilots use knots because:

• International standard
• Compatible with nautical charts
• Air traffic control uses knots
• Wind speeds reported in knots

Water current speeds

Ocean currents

Current	Typical speed (knots)
Gulf Stream	2-4
Kuroshio	2-3
California	0.5-1
Agulhas	3-4

Tidal currents

Location	Speed (knots)
Open ocean	0.5-1
Coastal areas	1-3
Narrow channels	3-8
Extreme areas	8-16

Quick mental math

Knots to MPH (approximate)

Add 15% to knots:

• 10 knots ≈ 11.5 mph
• 20 knots ≈ 23 mph
• 30 knots ≈ 34.5 mph

MPH to knots (approximate)

Subtract 13% from mph:

• 10 mph ≈ 8.7 knots
• 20 mph ≈ 17.4 knots
• 30 mph ≈ 26 knots

Rule of thumb

Knots × 1.15 ≈ MPH MPH × 0.87 ≈ Knots

Frequently asked questions

Why don't cars use knots?

Cars use statute miles (in US/UK) or kilometers because road distances are measured in those units. Nautical miles only make sense for navigation using latitude/longitude.

Is a knot faster than mph?

Yes, 1 knot equals 1.15 mph. So 100 knots is faster than 100 mph (100 knots = 115 mph).

Why do pilots use knots?

Aviation adopted nautical standards from maritime navigation. Knots work well with navigation charts and international air traffic control uses them universally.

How fast is 30 knots?

30 knots equals about 34.5 mph or 55.6 km/h. This is considered a strong breeze (Beaufort 6) and creates challenging sailing conditions.

What's a fast boat speed?

For recreational boats, 20-30 knots is fast. Racing sailboats can exceed 40 knots, and speedboats can reach 50-80+ knots.

Do submarines use knots?

Yes, all naval vessels including submarines measure speed in knots. Submarine speeds are often classified but generally range from 20-35+ knots.