What it does
Scientists write very big and very small measurements with prefixes: a kilometre is a thousand metres, a nanometre is a billionth of a metre. Each prefix is a power of ten:
| Prefix | Symbol | Power of ten |
|---|---|---|
| giga | G | 10⁹ |
| mega | M | 10⁶ |
| kilo | k | 10³ |
| centi | c | 10⁻² |
| milli | m | 10⁻³ |
| micro | µ | 10⁻⁶ |
| nano | n | 10⁻⁹ |
This page converts a value from one prefix to another and shows the rule: work out how many powers of ten apart the two prefixes are, and move the decimal point that many places. A prefix ladder shows the jump. The page does the arithmetic on the digits themselves, so 0.1 mm never turns into 0.000099999 m.
A second box adds two measurements. It changes both to the smaller prefix first, and refuses to add things that measure different quantities, like metres and seconds. That is the unit consistency check every equation must pass.
It fits the Class 9 science chapter Exploration: Entering the World of Secondary Science (SI units) and the Class 11 physics chapter Units and Measurement. Rounding to the right number of figures is in significant figures checker, and checking that both sides of an equation have the same units is in dimensional analysis checker.
How to use it
- Type a value, pick its prefix and unit, and pick the prefix to convert to.
- Read the answer, the steps, and the same answer in standard form (like 4.5 × 10⁻⁵).
- Follow the arrow on the ladder: going down to a smaller prefix makes the number bigger (point moves right); going up makes it smaller.
- In Add two measurements, type two values with their prefixes and units.
A worked example
The page starts with 2.5 km to cm.
- 1 km = 10³ m and 1 cm = 10⁻² m, so 1 km = 10³ ÷ 10⁻² = 10⁵ cm.
- Move the decimal point 5 places right: 2.5 → 250 000.
- So 2.5 km = 250 000 cm = 2.5 × 10⁵ cm.
In the adding box, 1.2 km + 350 m: change 1.2 km to 1 200 m, then 1 200 + 350 = 1 550 m.
Tips
- Capital and small letters matter: m is milli but M is mega; k (kilo) is always small.
- Prefixes for mass go on the gram, even though the SI base unit is the kilogram.
- The prefixes between kilo and milli (hecto, deca, deci, centi) are used less in science, except the centimetre.
Check yourself
Five fresh questions: three conversions, a prefix’s power of ten, and which quantities can be added. Nothing is saved.
FAQ
Why move the point and not multiply? It is the same thing: multiplying by 10³ moves the decimal point 3 places right. Moving the point is quicker and avoids rounding slips.
Is this the NCERT book? No. It covers the same topic with fibub’s own examples and questions. fibub is not part of NCERT.
Where the numbers come from
- SI prefixes and base units: BIPM, The International System of Units (SI Brochure), 9th edition, 2019. Pictures and questions written for fibub.
- Checked: conversions done on the digits as text match Python's decimal module for every prefix pair and 2 000 random values.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.