How to Calculate Decimal Numbers

Step-by-step

1. Write down the decimal values and check their units.
2. Enter the values and choose the required operation.
3. Calculate the result.
4. Check the number of decimal places and any rounding applied.
5. For financial or scientific work, verify the required precision and rounding convention.

Decimal places and rounding

Do not round intermediate values too early when precision matters. Follow the rounding rule required by the task and report the final precision clearly.

Money versus measurements

Currency calculations may require a fixed number of decimal places, while scientific measurements may need a different precision. Apply the rules appropriate to your context.

Worked examples

0.1 + 0.2 is 0.3. Computers store decimals in binary, which can produce tiny errors such as 0.30000000000000004, so the calculator rounds results to 12 significant digits.

For prices, 19.99 × 3 is 59.97. Round money only at the end, to the number of decimal places your currency uses.