Number Tools

Thirty-one tools for numbers, bases and identifiers

Bases and bit patterns, exact rounding and significant figures, primes and factorials, a number written out in words, and the check digits behind an IBAN, a VAT number, a barcode, an ISBN and a payment card. Each tool does one thing, shows its working where there is working to show, and says what it cannot do.

None of the arithmetic here is done in floating point. A spreadsheet rounds 2.675 to 2.67 because the number it is holding is very slightly less than 2.675; these tools hold the digits you typed and round to 2.68. That is the whole reason several of them exist, and the float inspector is there to show you exactly what your language is holding instead.

Everything runs inside this browser tab, compiled to WebAssembly. There is no server to send anything to, and none of the tools makes a network request while it works — which matters most for the two that take a card number and a national identity number.

Bases and machine numbers

Number base converter
Any base from two to thirty-six, with no ceiling on the number and the fraction included.

Roman numeral converter
Both ways, a whole column at a time, and it reads the clock-face spellings too.

Binary calculator
Adds, subtracts, multiplies and divides in base two, with the columns written out.

Hex calculator
The same arithmetic in base sixteen, which is how an address and an offset are written.

Bitwise calculator
AND, OR, XOR, NOT and the four shifts, with every value laid out as bits.

Two's complement converter
How a machine stores a negative number, in any width, with the range beside it.

IEEE 754 float converter
Why nought point one is not nought point one, shown as all fifty-five digits of what was stored.

Rounding and notation

Rounding calculator
Six rules side by side, in exact decimal arithmetic, and a column that still adds up.

Significant figures calculator
How many a number has, what it looks like rounded to three, and when the count is genuinely ambiguous.

Scientific notation converter
Scientific, engineering and written out at once — and the engineering exponent always names an SI prefix.

Numbers in words

Number to words converter
English, Slovak and Czech, with the scale words in the form the count actually asks for.

Words to number converter
Reads numbers written in words out of a document, and says when the figures beside them disagree.

Ordinal number converter
The English suffixes with their exceptions, and the Slovak and Czech endings in five cases.

Amount in words for invoices
The line under the figures on a document, with the currency in the right form and the rest of the line ruled out.

Fractions, percentages and digits

Percent to fraction converter
A percentage, a fraction and a decimal are one value written three ways; give any one and get the other two.

Decimal to fraction converter
The exact fraction, repeating decimals included — and the nearest sixteenth when a tape measure is what you have.

Digit sum calculator
The sum, the product and the digital root, with the divisibility rules for three, nine and eleven.

Primes and factors

Prime number checker and factoriser
Prime or not, the factorisation, every divisor — and it says when the answer is probable rather than proved.

GCD and LCM calculator
Both, for as many numbers as you give, with Euclid's working written out step by step.

Factorial calculator
The exact value, however many digits that takes — which is the one thing a pocket calculator cannot give.

Sequences and lists

Number sequence generator
Arithmetic, geometric, or whatever rule the terms you give it imply — padded and wrapped for a column of identifiers.

Fibonacci sequence generator
The terms, the one at any place however far along, and whether a number is one of them.

Number sorter
Sorts by value and reads both decimal marks — which is where a spreadsheet quietly gets a pasted column wrong.

Identifiers and check digits

Check digit calculator
Luhn, GTIN, ISBN, modulo eleven and the two ISO 7064 rules, with the working digit by digit.

IBAN validator and converter
The check that catches a mistyped account before the payment leaves — fifty-one countries, and the Slovak and Czech national forms.

VAT number format validator
Every European Union country's format, and the national check digit wherever this tool actually has the algorithm.

National ID number validator
The Slovak and Czech rules, historical exceptions included, on your own device and nowhere else.

Credit card number validator
The checksum and the issuer, and test numbers for a payment form — none of it leaving this device.

ISBN 10 and 13 converter
Both forms of a book, journal and sheet-music numbers too — and it refuses the conversion that has no answer.

Characters and codes

Unicode codepoint lookup
What exactly this character is, in every encoding and escape — and why the search found nothing.

ASCII table lookup
The chart with a search box: type the character, any of its four numbers, or half its name.

Questions

Why does this round differently from my spreadsheet?: Because it is not using floating point. A spreadsheet stores 2.675 as a binary fraction very slightly below 2.675, so rounding it to two places gives 2.67. These tools keep the digits you typed and round them as arithmetic says, which gives 2.68. Both answers are defensible and only one of them is the one you meant.
Does a valid check digit mean the number is real?: No, and every one of these tools says so on its own result. A check digit catches a mistyped digit and a pair swapped over. It cannot tell you that the account, the company, the card or the person exists — only the register that issued the number can do that, and reaching one would need a network request, which these tools deliberately never make.
Is what I type uploaded anywhere?: No. The tools are compiled to WebAssembly and run inside the browser tab. Nothing you type is sent to a server, and you can watch your browser's network panel while you use one to see that nothing leaves the page.
Can I use them in my own language?: The interface is in thirteen: English, German, Spanish, French, Portuguese, Italian, Russian, Ukrainian, Turkish, Polish, Czech, Slovak and Hungarian, and each writes numbers with its own decimal mark and grouping. The four tools that spell a number out in words offer three — English, Slovak and Czech — because spelling a number is a grammar rather than a translation, and a fourth language means a fourth grammar written by somebody who speaks it.

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