Formula of Speed: Speed = Distance / Time, Units, Examples

The formula of speed is $v = \frac{d}{t}$ , which reads speed = distance / time. Measure how far something travels along its actual path, divide by how long it took, and you have its speed. A bicycle that covers 90 m in 15 s is moving at 6 m/s.

Speed has no direction. It is never negative, and it does not care whether the path is straight, curved or doubled back. That makes it the easiest motion quantity to calculate and the one most students meet first, usually in Class 6 to Class 9 in India and in middle school science in the US. Some Indian books use s for distance and write v = s/t; this page uses d to keep distance and displacement apart.

Quick facts

Formula
$\text{speed} = \frac{\text{distance}}{\text{time}}$
SI unit
metre per second (m/s)
Everyday unit
km/h, where 1 m/s = 3.6 km/h
Dimensional formula
[M⁰ L¹ T⁻¹]
Type
Scalar: size only, never negative
Rearranged
$d = vt$ , $t = \frac{d}{v}$

The formula of speed explained

Terms in v = d / t
Symbol	Quantity	SI unit
$v$	Speed	m/s
$d$	Distance travelled along the path	m
$t$	Time taken	s

Distance here means the full length of the route, every metre the wheels or feet actually covered. If a dog runs 25 m to fetch a stick and 25 m back, the distance is 50 m. That 50 m goes into the speed formula. Velocity would use the displacement, which is zero for that run.

Speed physics formula questions usually give two of the three quantities. Cover the one you want and the other two show how to get it: distance over time for speed, speed times time for distance, distance over speed for time. The speed calculator on this page does the same rearrangement.

Speed formula physics examples

Example 1: a fast bowler

A cricket ball travels the 20.12 m length of the pitch in 0.50 s. Find its average speed in m/s and km/h.

$v = \frac{20.12}{0.50} = 40.24\ \text{m/s} \approx 40\ \text{m/s}$

In km/h: $40.24 \times 3.6 \approx 145\ \text{km/h}$ .

Example 2: a road trip, converting units

A car covers 150 km in 2.5 hours. Find its average speed in km/h and in m/s.

$v = \frac{150}{2.5} = 60\ \text{km/h}$

In SI units: $v = \frac{150\,000\ \text{m}}{9000\ \text{s}} = 16.7\ \text{m/s}$ . Check: 60 ÷ 3.6 = 16.7 m/s.

Example 3: finding distance

A student walks to school at a steady 1.5 m/s for 20 minutes. How far is the school?

t = 20 × 60 = 1200 s.

$d = vt = 1.5 \times 1200 = 1800\ \text{m} = 1.8\ \text{km}$

Unit conversions for speed

Common speed conversions
From	To	Multiply by
km/h	m/s	5/18 (or divide by 3.6)
m/s	km/h	18/5 (or 3.6)
cm/s	m/s	0.01
miles per hour	m/s	0.447

The 3.6 comes from 1000 m in a kilometre and 3600 s in an hour: 3600 / 1000 = 3.6. Board papers like the fraction 5/18 because it keeps the arithmetic exact. Written in base units, speed is metres per second, so in brackets it becomes [M⁰ L¹ T⁻¹], identical to velocity.

Types of speed

Uniform speed: equal distances in equal time intervals, however small. A train cruising on a straight stretch is close to this.
Non uniform speed: unequal distances in equal intervals, such as a car in city traffic.
Average speed: total distance divided by total time for the whole journey. See the average speed formula page for multi stage trips.
Instantaneous speed: the speed at one moment, which is what a speedometer shows. It equals the size of the instantaneous velocity.

On a distance time graph, speed is the slope. A straight graph line signals uniform speed and a curve means the speed is changing. Distance time graphs never slope downward, because distance cannot decrease.

Where students slip

Mixed units. Kilometres over seconds gives km/s. Convert first.
Minutes as decimals. 1 h 15 min is 1.25 h, not 1.15 h.
Averaging speeds. Two equal distances at 30 km/h and 60 km/h give 40 km/h on average, not 45 km/h.
Negative speed. There is no such thing. A minus sign belongs to velocity.

Typical values help you sense check: walking about 1.4 m/s, a sprinter about 10 m/s, a highway car about 30 m/s, sound in air about 343 m/s.

Frequently asked questions

What is the formula of speed in physics?

Speed = distance / time, written v = d / t. The SI unit is m/s.

What is the SI unit of speed?

The SI unit of speed is metre per second (m/s). In daily life km/h is common; divide km/h by 3.6 to get m/s.

Is speed a scalar or a vector?

Speed is a scalar. It has size only. Velocity is the vector that adds a direction.

How do you find distance from speed and time?

Multiply them: d = v × t. Make sure the time unit matches the speed unit, for example hours with km/h or seconds with m/s.

How is speed different from velocity?

Speed is built from total path length and never points anywhere. Velocity is built from displacement and points along it, so a velocity can be zero or negative while the speed is positive.