Number Converter — How to Use It Online for Free
The Number Converter converts numbers between Binary, Octal, Decimal and Hexadecimal — and converts Roman numerals in both directions. It is a study and programming companion: type in one system, read the same value in the others.
Each number system is a different lens: binary shows what the machine stores, hex is binary made readable, octal survives in file permissions, and Roman numerals live on in outlines and monuments. Converting by hand — dividing by 2 or 16 repeatedly — is slow and slip-prone; the converter makes checking homework or debugging a value a five-second job.
How to use the Number Converter
- Type the number in the box.
- Select the system you are typing in — Binary, Octal, Decimal, Hex or Roman.
- Read the value converted into the other systems.
- Copy the one you need.
A worked example
A programmer friend describes the value 255 as 'FF'. Type 255 as Decimal and the Hex reads FF — also the colour-code maximum for one channel, which is why pure red is written #FF0000.
Tips for better results
- When converting hex colours, remember each pair of digits is one channel: red, green, blue.
- Invalid digits are the usual error — binary accepts only 0 and 1, octal only 0–7.
- For exam practice, convert by hand first, then check here — the checking is what builds speed.
A note on online calculators
Online calculators are only as good as the numbers typed into them, so two habits matter. First, decide what the result should roughly be before you calculate — an expected range catches the classic errors, like a misplaced decimal or a rate entered per month instead of per year. Second, read the labels: many money mistakes are really direction mistakes (adding tax instead of removing it, dividing by the new value instead of the original). The calculators here show the full picture — not just the headline figure but the totals and splits behind it — so you can see whether the answer makes sense, and adjust the inputs until it does.
Common questions
Where is hexadecimal used? In colour codes (#FF5733 is a colour written in hex), memory addresses, and low-level programming. Programmers convert constantly; seeing all the systems together is the fastest way to build intuition for them.
How far do Roman numerals go here? Roman numerals suit the classic range (roughly 1–3999) — enough for chapter numbers, outlines, and the dates and inscriptions they are used for. Beyond that, historical notation becomes non-standard.
Do I need to sign up or install anything? No. The Number Converter is completely free, needs no account and nothing to install — it runs in your browser, and anything you type stays on your device.
One tool rarely finishes the whole job. The natural companions to this one are covered in the Age Calculator guide and the Unit Converter guide — between them, most calculation tasks can be handled end to end in the browser, with no installs and no accounts.