Unit, Date & Number Converters
Convert a measurement, a date, a time or a number from one form to another — metric to imperial, New York time to Tokyo time, a Gregorian date to a Hijri or Hebrew one, 2024 to MMXXIV, 0.375 to ⅜ — with the conversion factor or the rule shown. Free, no sign-up.
Unit, Date & Number Converters
32 tools · free, no sign-up
Number to Words Converter
Convert numbers to their written word form. Follow APA, Chicago, and AP style rules for when to spell out numbers vs. use numerals in academic writing.
Roman Numeral Converter
Convert numbers to Roman numerals and Roman numerals back to numbers — for outlines, chapters, dates, and page numbering.
Date Format Converter
Convert a date between APA, MLA, Chicago, ISO 8601, and international formats. Enter any date and get every academic and standard format at once.
Age Calculator
Calculate exact age from a date of birth — in years, months, and days, plus total days lived and days until the next birthday.
Date Calculator
Calculate days between two dates, or add and subtract days from a date — with weekdays-only counting for assignment and project deadlines.
Number Base Converter
Convert numbers between binary, octal, decimal, and hexadecimal — see all four bases at once with the conversion steps explained.
Unix Timestamp Converter
Convert Unix timestamps to human-readable dates and dates back to timestamps — seconds and milliseconds, in UTC and your local time.
Military Time Converter
Convert between 12-hour (AM/PM) and 24-hour military time — instantly, with a full conversion chart and how-to-say guide.
Words to Numbers Converter
Convert written numbers to digits — 'two hundred forty-six' becomes 246. Handles hyphens, 'and', millions, and decimals.
Scientific Notation Converter
Convert numbers to scientific notation and back — with E-notation, engineering notation, and the steps shown for homework.
Ordinal Number Converter
Convert numbers to ordinals — 1 to 1st, 22 to 22nd — and spell them out (twenty-second), with the suffix rules explained.
Unit Converter
Convert between metric and imperial units — length, mass, temperature, volume, area, and speed — with the conversion factor shown.
Time Zone Converter
Convert a time between cities and time zones — see what 3 PM in New York is in London, Tokyo, or any zone, with DST handled automatically.
Discord Timestamp Generator
Create Discord dynamic timestamps — pick a date and time and copy the <t:...> code for every display style, from relative time to full date.
Decimal to Fraction Converter
Convert decimals to simplified fractions (0.375 = 3/8) and fractions to decimals — with the simplification steps shown, including mixed numbers.
Time Calculator
Add and subtract hours, minutes and seconds, find the time between two clock times (overnight or across dates), total a list of times, and convert decimal hours.
Week Number Calculator
Find the ISO 8601 week number, week-year and week date of any date, the US Sunday-start week number, the dates of any week, and every week of a year in one table.
Hijri Date Converter
Convert Gregorian dates to the Hijri (Islamic) calendar and back in the Umm al-Qura or tabular calendar, with the Arabic date, month lengths and the year's Gregorian span.
Font Size Converter
Convert font sizes between pt, px, em, rem, %, mm, cm, inches and picas using CSS's 96 px per inch, with editable root and parent sizes and a chart of common sizes.
Regnal Year Converter
Convert regnal years such as 13 Cha. 2 to calendar dates and dates to regnal years for old statutes, with Julian and Gregorian dates and the 25 March legal year.
Data Storage Converter
Convert bits, bytes, kB/KiB, MB/MiB and larger units exactly, see why decimal and binary prefixes differ, and estimate transfer time at a chosen bandwidth.
Ancient Number Systems Converter
Converts numbers into Babylonian, Egyptian hieroglyphic, Maya, Attic Greek and Ionic Greek numerals, with sign tables and place-value notes.
Japanese Era Converter
Converts Gregorian dates to Japanese era (nengō) dates from Meiji to Reiwa and back, with exact era start dates and the first-year (gannen) rule.
Hebrew Calendar Converter
Convert Gregorian dates to Hebrew dates and back, with the sunset rule, leap years, month lengths, Hebrew script and the year's holiday dates.
Persian Calendar Converter
Convert Gregorian dates to Persian (Solar Hijri, Jalali) dates and back, with Persian script, leap years, month lengths and the March equinox that fixes Nowruz.
Julian Calendar Converter
Convert Julian (Old Style) dates to Gregorian (New Style) and back, with the day gap, dual dating, double years and the date each country adopted the Gregorian calendar.
Julian Day Calculator
Convert calendar dates and times to Julian Day, Modified Julian Day and Julian Day Number, or a JD or MJD back to a date, in the Gregorian, Julian or historical calendar.
Day of the Week Calculator
Find the weekday of any date from year 1 to 9999 in the Gregorian, Julian or a country's historical calendar, with Zeller's congruence and Doomsday working.
Chinese Zodiac Calculator
Find your Chinese zodiac animal, element and yin or yang from a birth date, using the real date of Chinese New Year for each year from 1900 to 2100.
Metric Prefix Converter
Convert between SI prefixes from quecto (10⁻³⁰) to quetta (10³⁰) for any unit, exactly, with scientific notation and the closest engineering prefix.
Energy Unit Converter
Convert energy exactly between joules, calories, kilocalories, kWh, BTU, electronvolts, ergs and foot-pounds, with thermochemical and IT calories kept apart.
Pressure Unit Converter
Convert pressure exactly between pascals, bar, atmospheres, torr, mmHg, inHg and psi, using the NIST definitions, with a table of your value in every unit.
Units, Times and Numbers
- Units. The Unit Converter for length, mass, temperature, volume, area and speed, the Energy and Pressure unit converters, the Metric Prefix Converter for milli to mega and beyond, the Data Storage Converter for KB versus KiB and transfer times, and the Font Size Converter for pt, px, em and rem.
- Times. The Time Zone Converter, Time Calculator, Military Time Converter, Unix Timestamp Converter and Discord Timestamp Generator, whose code shows each reader the time in their own zone.
- Numbers in words. Number to Words, Words to Numbers and the Ordinal Number Converter.
- Number forms. The Roman Numeral Converter, Number Base Converter, Scientific Notation Converter, Decimal to Fraction Converter and Ancient Number Systems Converter, which writes any number in Babylonian, Egyptian, Maya and Greek numerals.
Dates and Calendars
| You need… | Use |
|---|---|
| A date written in APA, MLA, Chicago or ISO 8601 form | Date Format Converter |
| Days, weeks or workdays between two dates; a date plus 90 days | Date Calculator |
| A person's exact age, or which weekday a date fell on | Age Calculator, Day of the Week Calculator |
| An ISO week number | Week Number Calculator |
| An Islamic, Jewish or Persian date | Hijri, Hebrew or Persian Calendar Converter |
| A pre-1752 British date, or an Old Style (Julian) date in a source | Julian Calendar Converter, with country adoption dates and dual dating |
| A date in a Japanese source or an English statute | Japanese Era Converter, Regnal Year Converter |
| A continuous day count for astronomy or archives | Julian Day Calculator |
| A birth year's animal sign | Chinese Zodiac Calculator, using the real Chinese New Year dates |
Converters for Writing
Several converters answer style questions as well as math ones. Style guides disagree on when to spell a number out and how to write a date:
| Question | APA 7 | Chicago 18 |
|---|---|---|
| Spell out numbers… | Zero to nine; numerals from 10 | Zero to one hundred, and round multiples |
| Number at the start of a sentence | Spell it out or rewrite the sentence | Spell it out or rewrite the sentence |
| Date in a reference | (2024, March 5) | March 5, 2024 |
MLA 9 spells out numbers that take one or two words and writes dates day-month-year in the works-cited list (5 Mar. 2024). The Number to Words Converter applies the APA, Chicago and AP number rules, and the Date Format Converter writes a date in each style's form.
Unit conversions use exact definitions where they exist — an inch is exactly 2.54 cm, a pound exactly 0.45359237 kg — so rounding happens once, at the end. Time zone conversions follow the IANA time zone database built into your browser, which includes daylight saving rules; check dates near a clock change, when an hour can be skipped or repeated. Calendar conversions such as Hijri dates can differ by a day from a local announcement, because some communities set the month by sighting the moon. The converters run in your browser. For converting citations and identifiers rather than numbers — DOI to APA, BibTeX to RIS — see the citation converters and the Citation & Reference Tools shelf.
Frequently Asked Questions
- How do I convert Celsius to Fahrenheit?
- Multiply by 9/5 and add 32: 20 °C × 9/5 + 32 = 68 °F. To go back, subtract 32 and multiply by 5/9. The Unit Converter does both and shows the formula.
- What is 2024 in Roman numerals?
- MMXXIV: M + M = 2000, XX = 20, IV = 4. Roman numerals have no zero, and the standard form stops at MMMCMXCIX, or 3,999. The Roman Numeral Converter explains each part.
- How do I count only weekdays between two dates?
- Use the weekdays-only option in the Date Calculator. It counts Monday to Friday between the two dates; public holidays are not removed, so subtract any that fall in the range.
- What is a Unix timestamp?
- The number of seconds since 00:00:00 UTC on 1 January 1970, not counting leap seconds. Many systems use milliseconds instead, which gives a number three digits longer. The Unix Timestamp Converter handles both and shows UTC and your local time.
- How many bytes are in a kilobyte?
- It depends on the convention. In SI usage a kilobyte (kB) is 1,000 bytes, and a kibibyte (KiB) is 1,024 bytes; some operating systems still say KB for 1,024. The gap grows with each step — a terabyte is about 9% less than a tebibyte. The Data Storage Converter shows both.
- Why do some historical dates differ between sources?
- Britain and its colonies used the Julian calendar until 1752, when they moved to the Gregorian calendar and skipped 11 days, and the new year began on 25 March rather than 1 January. Sources therefore give dual dates such as 1 February 1731/32. The Julian Calendar Converter shows the day gap for each country.