Unit Conversion Calculator

Free unit converter for the length, weight, area, volume, and time units taught in elementary math. Shows the steps and handles decimals exactly, such as 2.5 m = 250 cm.

How to use

Choose a category: length, weight, area, volume, or time.
Pick the “from” and “to” units, then type a value.
Press “Calculate” to see the answer and steps (time also shows forms like “1 min 40 s”).

Examples

2.5 m = 250 cm
1.5 kg = 1500 g
100 s = 1 min 40 s

When to use it (grade level)

Unit conversion starts in 2nd grade with length and capacity and grows through the elementary years to weight, area, volume, and time. It is also a foundation for science, rates, and speed in middle school. This tool suits checking home study, confirming your work before a test, and untangling units you find tricky.

For a question like “2.5 m is how many cm?”, you can confirm the exact answer with steps even when decimals are involved. It shows not just the result — 2.5 m = 250 cm, or 1.5 kg = 1500 g — but why it works.

How to work it out yourself

The basic idea is to think about how many of the smaller unit fit into one of the larger unit. Since 1 m = 1000 mm, 1 kg = 1000 g, and 1 L = 1000 mL, you multiply when going from a larger unit to a smaller one and divide when going the other way.

For example, to change 2.5 m to mm: 1 m = 1000 mm, so 2.5 × 1000 = 2500 mm. Going the other way, to change 1500 g to kg: 1 kg = 1000 g, so 1500 ÷ 1000 = 1.5 kg.

The unit “staircase” and why area and volume scale differently

Length units line up on a staircase: k (kilo), h (hecto), da (deca), the base unit, d (deci), c (centi), m (milli). Each step to the right is ten times finer, and each step to the left is ten times larger. Because c means one hundredth, 1 m = 100 cm, and since 1 cm = 10 mm, we get 1 m = 1000 mm.

Area, however, scales differently. Even though 1 m = 100 cm, we have 1 m² = 10000 cm². That is because area spreads in two directions. A 1 m² square is 1 m by 1 m, which is 100 cm by 100 cm, so its area is 100 × 100 = 10000 cm². The factor 100 that we multiply once for length is applied twice for area: 100 × 100 = 10000.

Volume adds a third direction, so the factor is applied three times. Even with 1 m = 100 cm, we get 1 m³ = 100 × 100 × 100 = 1000000 cm³. In capacity units, 1 m³ = 1 kL = 1000 L, and since 1 L = 1000 mL, 1 kL = 1000000 mL. The key point: length uses 10, area uses 10 × 10, and volume uses 10 × 10 × 10.

Common mistakes

The most common slip is using the length factor for area or volume. Because 1 m = 100 cm, learners sometimes write 1 m² = 100 cm², but the correct value is 1 m² = 10000 cm². Remember: multiply twice for area and three times for volume.

Another is mixing up multiplication and division. Larger-to-smaller units multiply; smaller-to-larger units divide. When unsure, write out “1 cm = 10 mm” (how many of the smaller fit in one larger) before you calculate.

Time needs extra care because it is not base ten: 60 seconds make a minute and 60 minutes make an hour. So 100 seconds does not divide evenly: 100 ÷ 60 = 5/3 minutes (about 1.6667). For cases like this the tool shows a reduced fraction and a rounded approximation, plus a combined form such as “100 s = 1 min 40 s”.

FAQ

Can I enter decimals?

Yes, up to 10 decimal places. Enter values like 2.5 m or 1.5 kg directly.

How are answers that don’t divide evenly shown?

For cases like time that don’t divide evenly, the tool shows a reduced fraction (e.g. 5/3) and a rounded approximation to four decimal places. Time also adds a combined form such as “1 min 40 s”.

Which units are supported?

The first version covers the elementary-math units: length (mm–km), weight (mg–t), area (cm²–km²), volume (mL–kL), and time (seconds–days).