Octal to Decimal

Input and output

Use digits 0–7, an optional leading plus or minus sign, an optional 0o prefix and one optional decimal point. Spaces, tabs and line breaks group a single number and are removed: 1 7.2 5 means 17.25. They do not separate a batch. Leading zeros are accepted. A leading point or a trailing point is accepted when at least one digit is present. Commas, exponent notation and digits outside the octal alphabet are rejected; an error clears the old result.

The result is a decimal number, not decoded text or file bytes. The optional hexadecimal equivalent represents the same value. This octal to decimal calculator processes one number at a time, with at most 1,000 octal digits and at most 10,000 total input characters including whitespace. It requires no account and sends no conversion input to a service.

How the calculation works

To convert octal to decimal, multiply every digit by its positional power of eight and add the contributions. Powers start at zero immediately before the point and become negative after it. The steps list contains one contribution per input digit, followed by the total. A minus sign is applied to the total.

Calculation uses browser BigInt arithmetic. A fractional denominator is a power of eight, so its decimal expansion terminates. The converter produces that expansion without selecting a rounding mode. This is an octal to decimal converter for numbers, rather than a fixed-width signed machine-word interpreter.

In a limited, directly observed comparison of online tools, we submitted the same long input, 400000000000000001, and the same fractional input, 17.25. Anonymous records follow in the saved audit's order, not as a claim about every online converter. Tool A returned 9007199254740993 and 15.328125. Tool B: outputs not obtained because interaction was interrupted; no capability conclusion. Tool C displayed 90071992547409 for the long input while its intermediate line displayed 9007199254740992 + 1; the fractional output was 15.328125. This records the visible result, not the internal cause. Tool D returned 9007199254740993 and 15.328125. Tool E returned 9007199254740993 and rejected the fraction with Invalid octal — use only digits 0–7. Record F was an article without a conversion input, so input testing was not applicable. Tool G returned 9007199254740992 and rejected the fraction with Not a octal number. Record H was a question-and-answer page without a conversion input, so testing was not applicable. Tool I returned 9007199254740992 and 15. Tool J eventually displayed 9007199254740992 for the long request; its fractional response was not obtained unambiguously, because the old result remained visible after the input changed. The reference values 9007199254740993 and 15.328125 were independently calculated locally using Python integer arithmetic and an exact fraction, 981/64. These are observations for the stated inputs only, not measured maximum lengths, a claim about all tools, or proof that an undocumented capability is absent.

Frequently asked questions

Does this octal to decimal calculator accept fractions?

Yes. A point separates the integer and fractional digits. Every digit must still belong to the octal alphabet.

Can I convert octal to decimal with spaces?

Yes. Whitespace groups one value and is removed before conversion. Use one number per run.

Why can a long number give different answers elsewhere?

A displayed answer may differ because of an implementation's numeric representation, accepted syntax or rendering. The observations above establish displayed outputs only; they do not identify the internal cause. This page computes the value with integer arithmetic.

Do I need to register?

No. Conversion and copying run in the browser. There is no saved history.