What is a speed calculator?
A speed calculator solves the simplest equation in physics: v = d/t. Speed equals distance divided by time. The three values are tied together so tightly that knowing any two of them gives you the third. The Speed Calculator is the version of that equation you can type into instead of doing the arithmetic on a phone calculator and then converting the units afterwards.
Three modes. Pick which variable you want to solve for: speed, distance, or time. Type the other two. Read the answer in whatever unit makes sense. The calculator handles every unit conversion under the hood — five speed units (mph, km/h, m/s, ft/s, knots), four distance units, three time units — so a problem stated in "miles in minutes" and answered in "kilometres per hour" requires no extra work on your part.
How to use the Speed Calculator
The page has three input rows. Each is a number plus a unit dropdown.
- Pick the solve mode at the top: speed, distance, or time. The chosen variable becomes the output; the other two become inputs.
- Enter the two known values. Pick the right unit from each dropdown — the calculator handles all conversions internally, so you can mix and match (miles for distance, minutes for time, kilometres-per-hour for the answer).
- Read the result. The headline value is in the most common unit for that variable; below it, a small panel shows the same answer in other useful units.
- For time results, the calculator auto-picks a readable unit — seconds for short durations, minutes for medium, hours for long, days for very long.
All math runs in your browser. Nothing is sent to a server, and you don't need to sign up. There's also no "convert" button — the result updates as you type, the same way a spreadsheet would.
The formula and its three forms
Speed is distance per unit of time. Rearranging that one equation gives you three problems you can solve.
Solve for speed: v = d ÷ t
Solve for distance: d = v × t
Solve for time: t = d ÷ v
Worked example: someone drives 60 miles in 45 minutes. How fast were they going on average?
- Distance: 60 miles
- Time: 45 minutes = 45 ÷ 60 = 0.75 hours
- Speed: 60 ÷ 0.75 = 80 mph
- In other units: 128.75 km/h, 35.76 m/s, 117.33 ft/s, 69.51 knots
The catch with v = d/t is that the units have to agree. Miles and hours give miles per hour. Metres and seconds give metres per second. Miles and minutes give a number that isn't a standard speed unit and needs to be converted. The Speed Calculator handles the unit alignment automatically, but it's worth knowing what's happening underneath — when a textbook gives you "240 km in 3 hours," the answer is 80 km/h only because both inputs use compatible units.
The equation assumes constant speed. For real-world questions where speed changes (a car accelerating from a stop, a runner negative-splitting a marathon), v = d/t gives you the average speed across the whole interval, not the speed at any specific moment. For accelerating motion, you'd integrate or use kinematic equations from physics. For everyday "how long does this trip take" planning, average speed is what you want.
Converting between speed units
Five speed units come up enough to matter. Each is just a different way of writing the same physical quantity.
| From | To mph | To km/h | To m/s | To ft/s | To knots |
|---|---|---|---|---|---|
| 1 mph | 1.000 | 1.609 | 0.447 | 1.467 | 0.869 |
| 1 km/h | 0.621 | 1.000 | 0.278 | 0.911 | 0.540 |
| 1 m/s | 2.237 | 3.600 | 1.000 | 3.281 | 1.944 |
| 1 ft/s | 0.682 | 1.097 | 0.305 | 1.000 | 0.592 |
| 1 knot | 1.151 | 1.852 | 0.514 | 1.688 | 1.000 |
The handy approximations: kilometres per hour is roughly 60% of miles per hour (or mph × 1.6 gives km/h). Metres per second is roughly mph × 0.45 (or m/s × 2.2 gives mph). Knots are 15% larger than mph, because a nautical mile is 15% longer than a statute mile.
Knots deserve a paragraph. One knot is one nautical mile per hour, where a nautical mile is defined as one minute of arc of latitude along any meridian — about 1.852 km, or 6,076 feet. The unit shows up in aviation and maritime work because navigation by latitude and longitude is naturally angular, and "knots" maps directly onto how many minutes of latitude you cover in an hour. Modern GPS has made the historical convenience less critical, but the units persisted and remain standard in those fields.
Reference: how fast is what?
Numbers in isolation aren't useful. Below, the speed of common things in mph and km/h, so the result your calculation produces has a place to sit.
| What it is | mph | km/h |
|---|---|---|
| Glacier (typical flow) | 0.00001 | 0.00002 |
| Garden snail | 0.03 | 0.05 |
| Walking pace (average) | 3.1 | 5.0 |
| Brisk walk | 4.0 | 6.4 |
| Easy jog | 5.0 | 8.0 |
| Recreational running | 6 to 8 | 10 to 13 |
| Marathon world record pace (men) | 13.2 | 21.2 |
| Cycling, recreational cruise | 12 to 15 | 19 to 24 |
| Cycling, racing | 25 to 30 | 40 to 48 |
| Cheetah (sprint) | 70 | 113 |
| Highway driving, US | 65 to 75 | 105 to 121 |
| Highway driving, Autobahn unrestricted section | ~100 to 130 | ~160 to 210 |
| Commercial jet cruise | 550 | 885 |
| Speed of sound (sea level, 20 °C) | 767 | 1,235 |
| Concorde (cruise) | 1,354 | 2,179 |
| International Space Station (orbit) | 17,500 | 28,000 |
| Earth's orbital speed around the Sun | 66,600 | 107,200 |
| Speed of light (in vacuum) | 670,616,629 | 1,079,252,849 |
Speed of light is the universal speed limit. No object with mass can reach it. The numbers above the speed of sound are where you start to see physics get strange — supersonic, hypersonic, orbital, relativistic. The Speed Calculator's math is classical, valid up to about 10% of light speed; beyond that, special relativity adds corrections.
Speed limits around the world
Most countries set a few different limits — urban, rural, motorway — and the numbers vary by enough that "the speed limit" isn't a universal answer. A quick comparison of motorway limits gives a sense of the spread.
| Country | Motorway limit | Urban limit |
|---|---|---|
| Germany (Autobahn, restricted sections) | 130 km/h (81 mph) advisory, unrestricted otherwise | 50 km/h (31 mph) |
| United Kingdom | 70 mph (113 km/h) | 30 mph (48 km/h) |
| United States (most states) | 65 to 75 mph (105 to 121 km/h) | 25 to 35 mph (40 to 56 km/h) |
| Texas (US-130, Austin region) | 85 mph (137 km/h) — highest posted in the US | — |
| France | 130 km/h (81 mph), 110 km/h in rain | 50 km/h (31 mph) |
| Italy | 130 km/h (81 mph), 150 km/h some sections | 50 km/h (31 mph) |
| Australia | 110 km/h (68 mph) most states; 130 km/h NT | 50 km/h (31 mph) |
| Japan | 100 km/h (62 mph) | 40 km/h (25 mph) |
| Brazil | 110 km/h (68 mph) | 60 km/h (37 mph) |
| India | 100 to 120 km/h (62 to 75 mph) | 40 to 50 km/h (25 to 31 mph) |
| Isle of Man | No general limit on rural roads | 30 mph (48 km/h) |
The Autobahn isn't actually "no speed limit" — about 30% of the network has posted limits, and the rest has a 130 km/h advisory. Driving above the advisory is legal but if you crash, insurance can argue you forfeited some of your liability protection. The Isle of Man is one of the few places on Earth with no general posted limit on rural roads.
Running pace, the inverse of speed
Runners think in pace, not speed. Pace is time per unit distance — the inverse of speed. A pace of 8:00/mi means 8 minutes per mile, equivalent to 7.5 mph.
Convert mph to pace (minutes per mile): pace = 60 ÷ mph
Convert pace to mph: mph = 60 ÷ pace_in_minutes
A few reference pairs: 12:00/mi = 5 mph (brisk walk), 10:00/mi = 6 mph (very easy jog), 8:00/mi = 7.5 mph (recreational pace), 6:00/mi = 10 mph (competitive recreational), 5:00/mi = 12 mph (sub-elite), 4:35/mi = 13.1 mph (marathon world record pace for men).
The Speed Calculator returns speed. To get pace, divide 60 by the mph result, or use the dedicated pace calculator linked below — it handles the minutes-and-seconds formatting better, since pace is conventionally written as 7:30/mi rather than 7.5 min/mi.
Speed versus velocity
Both words describe how fast something is moving, but physics distinguishes them. Speed is a scalar — just a magnitude. Velocity is a vector — magnitude plus direction.
Two cars travelling at 60 mph in opposite directions have the same speed but opposite velocities. A car driving around a circular track at a constant 50 mph has constant speed but constantly changing velocity (because the direction keeps changing). For most everyday questions ("how long does this drive take?"), you don't need the distinction — speed is enough. Physics homework problems often require velocity vectors, especially anything involving acceleration, forces, or momentum.
The Speed Calculator solves for speed. If you need a velocity vector — speed plus direction — you'd typically break it into x, y, (and z) components using trig and solve each one separately.
Why average speed is usually less than the speed limit
The speedometer in a car shows instantaneous speed: how fast at this moment. Average speed is total distance divided by total time, which includes every stop, every slowdown, every acceleration. A 60-mile drive that takes 1.5 hours has an average speed of 40 mph, even if the cruise sections were at 70 mph.
For trip planning, you can usually estimate average speed at 15-20% below the posted speed limit on highway sections, and 30-40% below in urban driving. A trip estimated at "60 miles at 60 mph = 1 hour" almost never takes 1 hour in practice — traffic lights, merges, fuel stops, and traffic add up. Google Maps and Waze incorporate live and historical traffic data, so for actual road predictions they usually beat raw v = d/t math by a wide margin.
For physics problems and idealised scenarios — a frictionless puck, a constant-speed train, a steady-state cyclist — v = d/t is exact. For real-world planning, treat the result as a lower bound on time and add a buffer.
Related calculations
Speed-distance-time math overlaps with several adjacent problems.
- Length Converter — convert between miles, kilometres, metres, feet, and the rest. Useful as a preliminary step when distance and speed are stated in different unit families.
- Temperature Converter — pairs with speed for physics problems involving heat, motion, and gas laws.
- Density Calculator — another v = something equation; computes mass per unit volume.
- mL to fl oz Converter — volume conversion for fuel consumption and capacity problems.
- Dew Point Calculator — useful when speed-time problems involve weather (cross-country flights, sailing, outdoor running plans).
- Heat Index Calculator — pairs with running pace calculations for hot-weather training.
Frequently asked questions
What's the formula for speed?
Speed = distance ÷ time. Three rearranged forms: v = d/t (solve for speed), d = v × t (solve for distance), t = d/v (solve for time). The formula assumes constant speed. For motion that changes pace, the result is average speed across the whole interval, not the speed at any single moment. For accelerating motion (a car from a stop, a falling object), use the kinematic equations from physics — speed itself isn't enough.
How do I convert mph to km/h in my head?
Multiply mph by 1.6, or add 60% to the mph value. So 60 mph is roughly 60 + 36 = 96 km/h (exact: 96.56 km/h). Going the other way: km/h ÷ 1.6, or subtract about 37% from km/h. 100 km/h is roughly 100 − 37 = 63 mph (exact: 62.14 mph). Both rules of thumb are accurate to within 1% across normal driving speeds.
What's the difference between speed and velocity?
Speed is just magnitude — how fast. Velocity is magnitude plus direction. Two cars going 60 mph north and 60 mph south have the same speed but opposite velocities. For everyday "how long does this take" calculations, speed is enough. Physics problems involving forces, acceleration, or momentum usually need velocity vectors, broken into x, y, (and sometimes z) components.
What's a knot, exactly?
One knot is one nautical mile per hour. A nautical mile is defined as one minute of arc of latitude along a meridian — about 1.852 km, or 6,076 feet. The unit is standard in aviation and maritime work because navigation by latitude and longitude is naturally angular, and knots map cleanly onto how many minutes of latitude per hour you're covering. 1 knot equals 1.151 mph or 1.852 km/h.
Why is average speed always less than the speedometer reading?
The speedometer shows instantaneous speed — at this moment. Average speed is total distance divided by total time, which includes stops, slowdowns, and accelerations. A drive that holds 70 mph on the highway but stops for 10 minutes at a gas station has an average speed well below 70. For trip-time predictions, expect average speed about 15-20% below the cruise speed on highways and 30-40% below in cities.
How do I convert pace to speed for running?
Speed (in mph) = 60 ÷ pace_in_minutes. So 8:00 per mile pace = 60 ÷ 8 = 7.5 mph. Going the other way: pace = 60 ÷ speed. 6 mph = 60 ÷ 6 = 10:00 per mile pace. The conversion in km is identical with km/h instead of mph: 4:00 per km pace = 60 ÷ 4 = 15 km/h. Conventional running notation writes pace as "7:30/mi" rather than "7.5 min/mi" — the minutes and seconds are easier to read than a decimal.
How accurate is the Speed Calculator for real-world trip planning?
The arithmetic is exact for constant-speed scenarios. For real trips, the limit is the input — traffic, weather, route choice, stops, and fuel introduce 10-30% variance. Use the calculator's result as a baseline and add buffer time. Mapping apps (Google Maps, Waze, Apple Maps) incorporate live traffic and historical data and are usually more accurate than pure v = d/t math for actual road travel. The calculator is most useful for physics problems, hypothetical estimates, and back-of-envelope checks.
Does the calculator work offline?
Once the page is loaded, yes. All math runs in your browser; nothing is sent to a server during calculation. If you lose your connection while the tab is open, the page keeps working. You only need a connection the first time you visit, to download the few kilobytes of code that drive the page.