Speed Calculator

Speed	Trip Time	vs Current
Enter a distance above to see comparison

Stop	Distance	Leg Time	Cumulative
No stops added yet — use the form above

Step 1 — Enter Speed

Choose Your Unit

Type any speed value and select your preferred unit — mph, km/h, m/s, ft/s, knots, or Mach. Use the preset chips for common real-world speeds, or drag the logarithmic slider for a wide range from 0.1 to 25,000 mph.

Step 2 — Explore Physics

Analyze the Physics

Switch to the Physics Lab tab to adjust object mass and road surface. See stopping distances for dry, wet, and icy roads side-by-side, plus kinetic energy and impact force. The Chart.js visualization shows how stopping distance scales with speed.

Step 3 — Plan Your Trip

Calculate Trip Time

Head to the Trip Planner tab, enter your distance, and get an instant travel time estimate. See how trip time changes at different speeds, set a departure time for ETA, and add multiple stops with the waypoint tracker.

Basics How do I convert mph to km/h?

Multiply mph by 1.60934. For example, 60 mph × 1.60934 = 96.56 km/h. This calculator does the conversion automatically in real time — just enter your speed and all units update simultaneously.

Advanced Why does stopping distance increase so rapidly with speed?

Because stopping distance has two components: reaction distance (linear in speed) and braking distance (proportional to v²). Going from 30 mph to 60 mph doubles reaction distance but quadruples braking distance. At 60 mph on a dry road, total stopping distance is roughly 240 ft — more than 4× the 55 ft needed at 30 mph.

Basics What is Mach 1 and why does it matter?

Mach 1 is the speed of sound — approximately 767 mph (1,235 km/h) at sea level and 15°C. As an object approaches Mach 1, a shock wave builds up, creating the sonic boom. Supersonic aircraft (Mach >1) must be specially designed to handle this pressure wave. The Mach number changes with altitude because air temperature (and hence the speed of sound) decreases with height.

Basics How is kinetic energy calculated, and why does it matter for crashes?

KE = ½mv². At 65 mph a 1,500 kg sedan carries about 633 kJ of kinetic energy — equivalent to detonating roughly 150 g of TNT. In a crash, all this energy must be dissipated (through crumple zones, braking, etc.). Doubling speed quadruples KE, which is why high-speed crashes are so much more destructive.

Advanced How do knots differ from mph?

One knot equals one nautical mile per hour, where a nautical mile (1,852 m) is based on one arc-minute of Earth's latitude. 1 knot = 1.151 mph = 1.852 km/h. Knots are used in aviation and maritime contexts because nautical miles simplify navigation using degrees of latitude/longitude.

Advanced Why does ice increase stopping distance so much?

The coefficient of kinetic friction on ice is around 0.1, compared to 0.7 for dry asphalt — seven times lower. Since braking distance = v²/(2μg), an ice surface requires ~7× more braking distance than dry road. At 65 mph, a dry-road stop of ~200 ft becomes ~1,400 ft on ice — over a quarter mile.

Basics How is the trip time calculated?

Trip time = distance ÷ speed. For example, 100 miles at 65 mph takes 100/65 ≈ 1.538 hours = 1 hour 32 minutes. This calculator also lets you input a departure time to compute an estimated arrival time (ETA), and the speed comparison table shows how modest speed differences affect overall trip time.

Basics What is the speed of light, and what happens at relativistic speeds?

The speed of light in a vacuum is ≈299,792,458 m/s (670,616,629 mph). As objects approach even a small fraction of this (≥0.1c ≈ 67 million mph), relativistic effects like time dilation and length contraction become measurable. This calculator flags relativistic speeds because classical Newtonian physics breaks down and Einstein's special relativity must be applied for accurate results.

Speed Conversion

1 mph = 1.60934 km/h = 0.44704 m/s

Multiply mph by 1.60934 for km/h, or by 0.44704 for m/s. For knots, multiply mph by 0.86898.

Kinetic Energy

KE = 1/2 x m x v^2

Energy doubles when mass doubles, but quadruples when speed doubles. Use SI units (kg, m/s) for result in Joules.

Stopping Distance

d = v x t_r + v^2 / (2 x mu x g)

Reaction distance (v x t_r) plus braking distance. Friction coefficient mu varies: dry ~0.7, wet ~0.4, ice ~0.1.

Trip Time

t = d / v

Distance divided by average speed. Small speed increases save proportionally more time on longer journeys.

Velocity Speed with direction. Scalar speed has no direction; vector velocity does. Measured in m/s, mph, or km/h.

Mach Number The ratio of object speed to the local speed of sound (~343 m/s at sea level). Mach 1 = sonic; greater than 1 = supersonic.

Kinetic Energy Energy an object possesses due to motion. Quadruples when speed doubles, making high-speed impacts disproportionately destructive.

Friction Coefficient Dimensionless number representing grip between surfaces. Dry asphalt ~0.7, wet road ~0.4, ice ~0.1.

Knot One nautical mile per hour (1 kt = 1.852 km/h). Used in aviation and maritime navigation.

Pace Inverse of speed, expressed as time per unit distance. Useful for runners: minutes per mile or per kilometre.

60 mph x 1.60934 = 96.56 km/h. This is close to the 100 km/h speed limit used in many countries outside the US.

v = 29.06 m/s, mu = 0.4, t_r = 1.5s. Reaction distance = 29.06 x 1.5 = 43.6 m. Braking distance = 29.06^2 / (2 x 0.4 x 9.81) = 107.6 m. Total = 151.2 m (496 ft).

v = 29.06 m/s. KE = 0.5 x 1,500 x 29.06^2 = 633,370 J (633 kJ). That is enough energy to lift a 1-tonne object 64 meters into the air.

Speed vs. Velocity

In everyday speech "speed" and "velocity" are interchangeable, but in physics they differ: speed is a scalar (magnitude only), while velocity is a vector (magnitude and direction). A car travelling in a circle at a constant 60 mph has constant speed but changing velocity, because its direction keeps changing.

The Physics of Stopping

When a driver perceives a hazard, they first experience reaction time (~1.5 seconds on average), during which the vehicle travels at full speed. After the brakes engage, kinetic energy is converted to heat through friction. The braking distance formula d = v²/(2μg) reveals two critical insights: stopping distance is proportional to the square of speed (so twice as fast means four times the distance), and inversely proportional to the friction coefficient (so wet or icy roads dramatically extend stopping distances).

Kinetic Energy and Crash Severity

The kinetic energy of a moving vehicle — KE = ½mv² — must be absorbed in every collision. A 1,500 kg sedan at highway speed (65 mph ≈ 29 m/s) carries about 633 kJ of kinetic energy. Car safety engineering (crumple zones, airbags) is fundamentally about extending the time over which this energy is dissipated to reduce peak forces on occupants. The quadratic relationship between speed and KE explains why speed limits have such an outsized effect on crash fatality rates.

Speed Units Explained

Different fields use different speed units for historical and practical reasons. Aviation uses knots because nautical miles (based on Earth's geometry) simplify navigation. Racing uses mph or km/h for accessibility. Science uses m/s as it fits into SI equations cleanly. Aerodynamics uses Mach numbers because air behaviour is governed by the ratio of object speed to the local speed of sound, not an absolute velocity. This calculator handles all these units interchangeably so you never need to do manual conversions.

Trip Planning Mathematics

The basic trip time formula is simply t = d/v — distance divided by speed. However small differences in average speed can have surprisingly large cumulative effects on long drives. Driving 75 mph instead of 65 mph on a 500-mile trip saves about 1 hour 10 minutes. The Trip Planner tab lets you visualise these trade-offs instantly, and the multi-stop waypoint tracker helps plan complex routes with realistic time budgets.

Related Calculators

Related Guides & Articles

Speed Reference Guide

Object / Scenario	Speed (mph)	Speed (km/h)	Mach
Average walking pace	3.1	5.0	0.004
World record 100 m sprint	27.8	44.7	0.036
Road bicycle (pro)	28	45	0.037
US highway speed limit	65–75	104–121	0.085–0.098
Top Fuel dragster	335	539	0.44
Speed of sound (sea level)	767	1,235	1.000
Concorde cruising	1,354	2,179	2.04
SR-71 Blackbird (record)	2,193	3,530	3.3
Low Earth orbit (ISS)	17,500	28,163	22.8
Earth escape velocity	25,020	40,270	32.6
Speed of light (vacuum)	670,616,629	1,079,252,848	874,030

How to Use This Calculator

Choose Your Unit

Analyze the Physics

Calculate Trip Time

Frequently Asked Questions

Formula & Methodology

Key Terms Explained

Real-World Examples

Convert 60 mph to km/h

Stopping Distance at 65 mph on Wet Road

Kinetic Energy of a 1,500 kg Car at 65 mph

Understanding Speed: A Complete Guide