You're standing on the deck of a ferry or maybe glancing at the seatback screen on a flight over the Atlantic. You see the speed: 22 knots. If you're like most people, your brain immediately hits a wall. Is that fast? Is it a crawl? Most of us think in miles per hour (mph) or kilometers per hour, so seeing "knots" feels like reading a dead language.
Honestly, it’s a weird unit. But it’s the global standard for anything that moves through air or water. If you want to convert knots to miles per hour, you aren't just doing a math problem; you're bridging the gap between ancient seafaring tradition and modern GPS logic.
The shortcut? One knot is about 1.15 mph.
If you just need a "good enough" estimate while you're staring at the ocean, just add 15% to the knot value. If the captain says you’re doing 20 knots, 10% is 2, and half of that is 1. Add them up, and you’re hitting roughly 23 mph. It’s not NASA-level precise, but it keeps you in the loop.
The math behind the maritime mystery
Why is it 1.15? Why can't sailors just use the same miles we use in our cars? The answer lies in the shape of the Earth itself. A knot is defined as one nautical mile per hour.
A standard "statute" mile (the one on your odometer) is an arbitrary 5,280 feet. It was originally based on 1,000 paces of a Roman legion. Nautical miles are much more scientific. One nautical mile equals exactly one minute of latitude. Since there are 60 minutes in a degree, and 360 degrees in a circle, the nautical mile is hardwired into the Earth's circumference.
To be exact, a nautical mile is 1,852 meters. A standard mile is roughly 1,609 meters. When you divide 1,852 by 1,609.34, you get the magic conversion factor: 1.15078.
So, the formal equation looks like this:
$$mph = knots \times 1.15078$$
If you’re a pilot or a professional navigator, you use the full decimal. If you’re just trying to figure out if your cruise ship is outrunning a storm, "times 1.15" is your best friend.
Why we still use knots in 2026
You’d think with the advent of ultra-precise satellite navigation and AI-driven flight paths, we would have standardized everything to kilometers or miles by now. We haven't. Navigation—whether you’re in a Boeing 787 or a sailboat—relies on charts based on latitude and longitude.
Because one nautical mile equals one minute of latitude, it makes chart work incredibly simple. If a navigator sees that they need to travel 10 minutes of latitude north, they know they have 10 nautical miles to go. If they tried to do that in mph, they’d be doing complex long-form division every time they looked at the map. It would be a disaster.
Technology hasn't replaced this; it has just automated the math. Even the most advanced flight management systems (FMS) in modern cockpits still output speed in knots because the entire world’s air traffic control infrastructure is built on it. If a pilot in Dubai and a pilot in New York are both told to maintain 250 knots, there is zero room for "unit translation" errors.
The "Dutchman" method and historical quirks
The term "knot" isn't a metaphor. It’s literal.
Back in the 17th century, sailors didn't have GPS or even reliable mechanical logs. They used a "chip log." This was basically a wooden board weighted to float upright, attached to a long rope. The rope had knots tied into it at specific intervals—traditionally 47 feet and 3 inches apart.
A sailor would throw the board overboard and flip a 28-second sandglass. As the ship moved forward, the board stayed still in the water, pulling the rope out. They’d count how many knots slipped through their fingers before the sand ran out. That number was their speed.
It was brilliantly simple. If 10 knots went through, they were going 10 knots.
Today, we don't use ropes, but the physics remains. When you convert knots to miles per hour, you’re translating a measurement of the Earth’s curves into a measurement of flat-land distance.
Real-world speed comparisons
To get a feel for the scale, look at these common speeds.
A typical walking speed is about 3 knots (3.4 mph). Most giant cargo ships cruise at around 20 to 24 knots, which sounds slow until you realize that’s about 27 mph—pushing hundreds of thousands of tons of steel through resisting water.
Nuclear submarines can reportedly exceed 30 knots (34.5+ mph) while submerged, though the exact figures are often classified. In the air, a Cessna might cruise at 120 knots (138 mph), while a commercial airliner at cruising altitude is often doing 450 to 500 knots (517 to 575 mph).
Note that wind speed is also measured in knots. If you hear a weather report about a 50-knot gust, that’s a 57 mph wind—enough to start ripping branches off trees and making driving dangerous.
Common pitfalls in the conversion
One thing people often mess up is the difference between "ground speed" and "airspeed." This is where the conversion gets tricky for travelers.
If your plane is doing 400 knots but flying into a 50-knot headwind, your speed relative to the ground is only 350 knots. When you convert that to mph, you have to decide which one you care about. Are you trying to figure out when you’ll arrive (ground speed) or how hard the engines are working (airspeed)?
Most "knot to mph" converters you find online assume you’re talking about a static measurement. They don't account for the fluid dynamics of water or air.
Another error is confusing the nautical mile with the "league." A league is actually three nautical miles. So if someone says they are "20,000 leagues under the sea," they’re talking about a distance that would wrap around the Earth several times. Jules Verne was a fan of the math, even if his readers weren't.
Practical ways to do the math in your head
Since you probably don’t want to pull out a calculator every time you hear a weather update, use these tiers:
The 10% Rule (Fast & Dirty)
Just add 10% to the number. 40 knots becomes 44 mph. You’ll be slightly under the real number, but it’s close enough for a casual conversation.
The "Plus a Seventh" Rule (Accurate)
Divide the knots by 7 and add that to the original. If you have 14 knots, 14 divided by 7 is 2. 14 plus 2 is 16. The actual answer is 16.11 mph. This is remarkably accurate for such a simple mental trick.
The "Double it and take a bit off" (Rough)
This is mostly for converting knots to km/h, but some people use it for mph by mistake. Don't do that. Stick to the 1.15 multiplier.
What experts say about the "Statute Mile"
Interestingly, some maritime experts, like those at the National Oceanic and Atmospheric Administration (NOAA), have occasionally discussed the obsolescence of the statute mile. In a perfect world, we’d all use the metric system or the nautical system. The statute mile is an outlier. It exists primarily because of land-surveying traditions in the US and UK.
However, because our entire highway infrastructure is marked in mph, we are stuck with this awkward conversion. It's a "legacy system" issue.
Moving forward with your measurements
Now that you know the "why" and "how" of converting knots to miles per hour, you can actually use it.
The next time you’re on a boat or plane, don't just look at the number. Use the "plus a seventh" trick. It’s a great way to keep your brain sharp and actually understand the velocity of your travel.
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If you're planning a trip or working on a maritime project, start by standardizing your units early. Use a dedicated GPS tool that allows you to toggle between units so you can see the relationship in real-time. This helps build an intuitive sense of speed that a calculator can't provide.
For those deep into DIY navigation or flight simulation, memorize the 1.15078 constant. It’s the only way to ensure your fuel calculations and arrival times don't leave you stranded. Whether you’re hobbyist or just curious, mastering this small bit of maritime math makes the world feel a little more navigable.