SI Units and Metric Conversions

What you’ll learn

Convert length, area, and volume with the correct powers.

បម្លែងប្រវែង ផ្ទៃក្រឡា និងមាឌដោយកត្តាត្រឹមត្រូវ។

Meaning and use

A measurement combines a number and a unit. Changing the unit changes the number, not the physical quantity. Area conversions square the length factor; volume conversions cube it. Convert quantities to compatible units before substituting them in a formula.

រង្វាស់មានលេខ និងឯកតា។ ប្ដូរឯកតាមិនប្ដូរបរិមាណពិតទេ។ ផ្ទៃក្រឡាប្រើការ៉េនៃកត្តាប្រវែង ហើយមាឌប្រើគូប។

Formulas

Length and time

\[1\,\mathrm{m}=100\,\mathrm{cm},\qquad1\,\mathrm{h}=3600\,\mathrm{s}\]

Area and volume

\[1\,\mathrm{m^2}=10^4\,\mathrm{cm^2},\qquad1\,\mathrm{m^3}=10^6\,\mathrm{cm^3}\]

Symbols and units

Symbol	Meaning	Unit or restriction
m, cm	Metre and centimetre	Length
m², cm²	Square metre and square centimetre	Area
m³, cm³	Cubic metre and cubic centimetre	Volume
h, s	Hour and second	Time

Conditions and limits

• Apply the conversion factor to the full dimensional unit.
• Do not multiply every conversion by 100: the dimension determines the power.
• ត្រូវសរសេរឯកតានៅគ្រប់ជំហានដើម្បីពិនិត្យការបម្លែង។

Worked examples

Length conversion

Convert 250 cm to metres.

1. Use \(1\,\mathrm{m}=100\,\mathrm{cm}\).
2. Calculate \(250/100=2.5\) m.

2.5 m

ពីសង់ទីម៉ែត្រទៅម៉ែត្រ ត្រូវចែក 100។

Area conversion

Convert 2 m² to cm².

1. Square the length factor: \(100^2=10000\).
2. Calculate \(2\times10000=20000\) cm².

20000 cm²

ឯកតាការ៉េត្រូវប្រើកត្តា 100²។

Common mistakes

Instead of	Use	Why
1 m² = 100 cm².	1 m² = 10000 cm².	Square the length conversion factor.
1 hour = 100 seconds.	1 hour = 3600 seconds.	There are 60 minutes, each with 60 seconds.

Practice

Solve these before revealing the worked solutions. Include units where relevant.

សាកល្បងដោះស្រាយមុនបើកមើលចម្លើយ។ សូមបង្ហាញជំហាន និងឯកតាដែលពាក់ព័ន្ធ។

1. Convert 3.5 km to m.
2. Convert 30 minutes to seconds.
3. Convert 1 litre to cubic centimetres.

Answers and steps

Show solutions / បង្ហាញដំណោះស្រាយ

1. 3500 m

   Multiply by 1000.

2. 1800 s

   Multiply by 60.

3. 1000 cm³

   A litre is one cubic decimetre.

Quick recap

• Keep a number and unit together.
• Square or cube length conversion factors as needed.
• Check unit compatibility before calculating.