Speed Calculator

Know any two of speed, distance, and time and this tool solves for the third using v = d / t, or convert a single speed value between mph, km/h, m/s, knots, and ft/s — every result shown with the formula worked out.

For personal planning and general reference — verify important results when needed.

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Choose a calculation type, enter your values, and click Calculate Now to see speed, distance, or time with step-by-step solutions.

One formula, three ways to use it

Speed, distance, and time are locked together by a single relationship — know any two and the third follows directly. The one thing that trips people up isn't the algebra, it's unit mismatches: mixing minutes with an hourly speed, or miles with a metric distance, throws the answer off by a wrong factor even though the arithmetic itself is correct.

Speed = Distance ÷ Time

Distance = Speed × Time

Time = Distance ÷ Speed

Covering 150 km in 2 hours works out to 150 ÷ 2 = 75 km/h. Flip it around: at 75 km/h, covering 300 km takes 300 ÷ 75 = 4 hours. Same relationship, just solved for whichever piece is missing.

Converting between speed units

Different fields default to different units — road speeds in mph or km/h, physics problems in m/s, aviation and marine navigation in knots — so converting between them comes up constantly.

Speed unit conversion factors
From To Multiply by
mphkm/h1.60934
km/hm/s0.27778
mphknots0.868976
m/sft/s3.28084

A useful mental shortcut: mph to km/h is roughly ×1.6, so 60 mph is close to 97 km/h — precise enough for a quick sanity check even before running the exact numbers.

Average speed isn't the same as the number on the speedometer

This calculator's speed mode gives an average over the whole distance and time entered, which is a different thing from instantaneous speed — what a speedometer or radar gun reads at one specific moment. A 240-mile trip completed in 4 hours averages exactly 60 mph, even if that included sitting in traffic at 10 mph for a stretch and cruising at 75 mph elsewhere. For planning purposes (fuel, arrival time, pacing) average speed is usually the number that actually matters.

Related tools for wheels and travel

Speedometer accuracy depends on actual tire diameter, not just the size printed on the sidewall — the tire size calculator works out real rolling diameter and how it shifts speedometer and odometer readings. And for cyclists dialing in a setup, the bike tire pressure calculator covers the other side of rolling performance.

Frequently Asked Questions

What is speed?

Speed is distance traveled per unit time — miles per hour (mph), kilometres per hour (km/h), or metres per second (m/s). It is a scalar quantity (magnitude only).

How do you convert between speed units?

1 mph ≈ 1.609 km/h; 1 km/h ≈ 0.2778 m/s. Multiply by the exact conversion factor and keep track of units to avoid errors.

What is the difference between speed and velocity?

Velocity includes direction; speed does not. '60 mph north' is velocity; '60 mph' alone is speed.

How do I find speed from distance and time?

Speed = distance ÷ time. Ensure distance and time units align — convert minutes to hours if distance is in miles and you want mph.

How do I use this speed calculator?

Enter any two of speed, distance, and time, select units, and click Calculate. The tool solves for the missing value with conversion options.

What is the difference between average speed and instantaneous speed?

Average speed is total distance divided by total time for an entire trip, smoothing out every stop and burst of acceleration along the way. Instantaneous speed is what a speedometer shows at one exact moment. A road trip with rest stops can average 45 mph overall while spending plenty of time at 70 mph on the highway.

Why do knots differ from mph?

A knot is one nautical mile per hour, and a nautical mile (about 1.15 statute miles) was originally defined from one minute of latitude along a meridian, not from any land-based mile. That different underlying distance is why 1 knot equals about 1.15 mph rather than lining up evenly.

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