Units of measurement

Metric units of length

Millimeters (mm):

We can use millimeters to measure things like the width of a small button, the length of an insect, or the size of tiny beads on a necklace.

Centimeters (1 cm=10 mm):

Centimeters are handy for measuring things that are a bit larger. For example, you can measure the length of your crayon, the width of a small toy car, or the height of your favorite action figure.

Meters (1 m = 100 cm):

Meters are great for bigger measurements. You can use meters to measure how tall you are, the length of your classroom, or the width of a soccer field.

Kilometers (1 km = 1000 m):

Kilometers are used for really long distances. You might use kilometers to measure the distance between your home and school, the length of a hiking trail, or the distance between cities on a map.

So, millimeters are for tiny things, centimeters for small things, meters for medium-sized things, and kilometers for really big things!

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Units of mass

Ounces (oz):

Ounces are used to measure the mass of small things. You can use ounces to measure the mass of a small toy, a piece of candy, or the weight of your favorite snack. It helps you understand how heavy or light things are.

Pounds (lb):

Pounds are larger than ounces and are great for measuring the weight of bigger things. For example, you can use pounds to measure the weight of your pet hamster, a backpack, or a bag of flour in the kitchen. So, ounces are for small, light things, and pounds are for heavier, larger objects. It's like having different tools for measuring the weight of things, depending on whether they are tiny or bigger.

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Units of time

1 min (minute) = 60 s (seconds)
1 h (hour) = 60 min

1.5 h = $1{1/2}$h = 1 h 30 min
1 h = 60 × 60 s= 3600 s

Units of time

1 min (minute) = 60 s (seconds)
1 h (hour) = 60 min

1.5 h = $1{1/2}$h = 1 h 30 min
1 h = 60 × 60 s= 3600 s

Units of time

1 min (minute) = 60 s (seconds)
1 h (hour) = 60 min

1.5 h = $1{1/2}$h = 1 h 30 min
1 h = 60 × 60 s= 3600 s

day = 24 h
week = 7 days (Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday)

month = from 28 to 31 days

Month	Number of days
January	31
February	28 or 29
March	31
April	30
May	31
June	30
July	31
August	31
September	30
October	31
November	30
December	31

year = 12 months = 365 days = 52 weeks 1 day
leap year = 12 months = 366 days = 52 weeks 2 days

A leap year is a year in which an extra day is added to the calendar in order to synchronize it with the seasons. In leap years, February 29th is added as leap day, which doesn't exist in a normal year (February has normally 28 days). A leap year occurs every 4 years - the year has to be evenly divided by 4 (2004, 2008, 2012), but not by 100 (1800, 1900, 2100). However, if it is divisible by 400, it's again a leap year (2000).

Metric units of length

m... meter
dm... decimeter
cm... centimeter

1 m = 100 cm = 10 dm
1 dm = 10 cm

Metric units of length

1 cm (centimeter) = 10 mm (millimeter)
1 dm (decimeter) = 10 cm
1 m (meter) = 100 cm = 10 dm
1 km (kilometer)= 1000 m

Metric units of length

1 cm (centimeter) = 10 mm (millimeter)
1 dm (decimeter) = 10 cm
1 m (meter) = 100 cm = 10 dm
1 km (kilometer)= 1000 m

Metric units of length

1 cm (centimeter) = 10 mm (millimeter)
1 dm (decimeter) = 10 cm
1 m (meter) = 100 cm = 10 dm
1 km (kilometer)= 1000 m

Customary units of length

1 inch (in) = 2.54 centimeters (cm)
1 foot (ft or ′) = 12 in = 30.48 cm
1 yard (yd) = 3 ft = 36 in = 0.91 meter (m)
1 mile (mi)= 1760 yd = 1.6 kilometer (km)

Metric units of area

1 cm² = 10 mm × 10 mm = 100 mm²
1 dm² = 10 cm × 10 cm = 100 cm²

1 m² = 10 dm × 10 dm = 100 dm² = 10000 cm²
1 km² = 1000 m × 1000 m = 1000000 m²

Metric units of mass

1 g (gram) = 1000 mg (milligram)
1 kg (kilogram)= 1000 g
1 t (ton) = 1000 kg

1 dkg (dekagram) =10 g
1 kg (kilogram)= 1000 g = 100 dkg

Customary units of mass

1 pound (lb) = 16 ounces (oz) ≅ 0.45 kilogram (kg)
1 oz ≅ 28 grams (g)
1.5 lb = 16 + 8 = 24 oz
$1/2$ lb = 8 oz

l (L)... liter
hl (hL)... hectoliter

1 hl =100 l

l (L)... liter
ml (mL)... milliliter

1 l =1000 ml

Speed Unit Conversion

Speed is measured as the distance travelled per unit of time. For example, if a car travels at 40 km/h, it means that it travels 40 km every hour (40 km in one hour, 80 km in two hours, 120 km in three hours, etc.). A commonly used unit in the United States is mph (miles per hour). Since speed is expressed as a combination of two units (distance divided by time), when converting between different units of speed, we need to pay attention to both units — distance and time — and determine how to convert each of them.

If we are moving at 2 m/s, it means that every second we travel 2 metres. How many metres will we travel in one hour? One hour has 3600 seconds.

In one hour, we will travel 7200 m. And how many kilometres will we travel in one hour? We know that 1 km is equal to 1000 m.

If a car is moving at 90 km/h, how many metres per second does it travel? In this case, we have to multiply 90 by 1000 to convert kilometres to metres (90 km = 90000 m). At the same time, we have to divide by 3600 because one hour has 3600 seconds:

So the car is travelling at 25 m/s. But what is its speed in km/min? As we know, one hour has 60 minutes. This means that in one minute it travels: