Converters
Units, measurements and currency, converted instantly.
Tools last updated
Unit converters that use exact, standards-based factors rather than rounded approximations. Type in one box and every other unit updates as you go — no convert button, no page reloads.
Most used
All 15 Converters
15 tools
Currency ConverterConvert between 30+ currencies using daily reference rates.Length ConverterMetres, feet, inches, miles and eleven other length units.Weight ConverterKilograms, pounds, stones, ounces and grams.Temperature ConverterCelsius, Fahrenheit, Kelvin and Rankine, side by side.Time ConverterSeconds to years, and everything in between.Speed Converterkm/h, mph, knots, m/s and the speed of sound.Area ConverterSquare metres, acres, hectares, square feet and more.Volume ConverterLitres, gallons, cups and spoons — US and imperial kept apart.Data Storage ConverterBytes to terabytes, with decimal and binary units separated.Shoe Size ConverterConvert shoe sizes between US, UK, EU and Japan, or work them out from foot length.Engine CC to HP ConverterConvert cc to litres and cubic inches, and estimate horsepower from engine size.Time Zone Meeting PlannerCompare cities hour by hour to find meeting times inside everyone's working day.Roman Numeral ConverterConvert numbers to Roman numerals and back, with the working shown.Number to WordsWrite numbers and money amounts in words, for cheques and invoices.Number Base ConverterConvert between binary, octal, decimal, hex and any base up to 36.
How these converters work, and where conversions go wrong
Unit conversion looks like simple multiplication, and most of the time it is. The mistakes come from units that share a name but not a size, and from quantities that cannot be converted exactly at all. The converters above are built to make those cases visible.
Exact by definition
The everyday imperial units are not separate measurements. Since an international agreement in 1959, the inch has been defined as exactly 25.4 millimetres and the pound as exactly 0.45359237 kilograms, so the Length Converter, Weight Converter, Area Converter and Speed Converter give exact answers, not approximations. The unit converters take your value to a single base unit and back out again, work at full precision, and round only what is displayed — so converting a number there and back returns what you started with.
Same name, different size
- Gallons, pints and cups. A US gallon is 3.785 litres and an imperial gallon is 4.546 — about 20% more. The Volume Converter lists US and imperial units separately so a recipe or a fuel figure is not converted with the wrong one.
- Tons. A metric tonne is 1,000 kg, a US short ton is 2,000 lb and a UK long ton is 2,240 lb. All three appear in the weight converter under their own names.
- Gigabytes. Drive makers count in steps of 1,000 and operating systems often count in steps of 1,024, which is why a 1 TB drive shows as 931 GB. The Data Storage Converter keeps the decimal and binary units apart.
Conversions that need more than a factor
Temperature scales have different zero points as well as different step sizes, so the Temperature Converter shifts as well as scales. Months and years have no fixed length, so the Time Converter uses the calendar average — 365.2425 days to a year and about 30.44 to a month — and says so. For the gap between two real dates, use the Age Calculator instead.
Estimates and reference data
Four tools here go beyond fixed factors, and each is clear about how far to trust it:
- The Currency Converter uses the European Central Bank's daily reference rates and shows the date of the rate. These are mid-market rates; a bank or card provider adds its own margin and fees. It is the one tool in this group that needs the network, and only the currency codes are looked up — the amount you type stays in your browser.
- The Shoe Size Converter uses the relationships the US, UK, EU and Japanese systems are built on. Individual brands can differ by up to a full size, so compare your foot length with the maker's chart.
- The Engine CC to HP Converter converts displacement exactly, but horsepower cannot be calculated from engine size — it gives a realistic range for each type of engine instead.
- The Time Zone Meeting Planner works out local times for the date you choose, so daylight saving changes and half-hour time zones are handled correctly.
Guides
- What your BMI means — and what it cannot tell youHow BMI is calculated, what the WHO categories mean, the healthy weight range for your height, and the real limits of BMI for individuals.
- Why a 1 TB drive shows only 931 GB — and other storage numbers explainedNobody stole your storage: drive makers and computers count in different units. Here is the maths, plus MB vs Mbps and a quick conversion list.
- How much paint do I need? Measuring a room properlyMeasure a room, work out the wall area, allow for doors, windows and coats, and turn it into the right number of tins — with metric and imperial examples.
- How to calculate an exact age in years, months and daysWhy dividing by 365 gives the wrong age, how to count years, months and days, what happens to 29 February birthdays, and how to find an age on a cut-off date.
- Dog years to human years: why the ×7 rule is wrongHow old a dog or cat really is in human terms, why size changes the answer, what a DNA study found, and a quick chart for small, medium, large and giant dogs.
- How much does it cost to charge an electric car?Work out the cost of a charge and the cost per mile or kilometre for an electric car, see why public rapid charging changes the picture, and compare with petrol.
- Recipe conversions: cups to grams, ounces, spoons and oven temperaturesConvert American, British and metric recipes: why cups to grams depends on the ingredient, US and UK pints, spoons, and oven temperatures in °C, °F and gas marks.
- Unix timestamps explained: seconds, milliseconds and time zonesWhat a Unix timestamp is, how to tell seconds from milliseconds, why dates come out a day wrong, and the year 2038 problem — with examples you can check.
- Currency conversion: the real rate, the bank's rate and the hidden feesWhat the mid-market exchange rate is, why your bank or card gives less, how to compare providers, and the card-terminal choice that costs travellers money.
- Height in feet and inches to centimetres, and backConvert a height between feet and inches and centimetres exactly, with a quick reference table and the mistakes that put conversions an inch out.
- Acres, hectares, square feet and local land units explainedConvert land and floor areas between acres, hectares, square metres and square feet, picture how big each one is, and handle local units such as ropani and cent.
- Running pace and speed: min/km, min/mile, km/h and mphConvert running pace to speed and back, switch between kilometres and miles, and work out a finish time for 5K, 10K, half marathon and marathon.
- Shoe size conversion: US, UK, EU and Japan — and why it variesConvert shoe sizes between US men's and women's, UK, European and Japanese systems, measure your foot properly, and understand why brands disagree.
- Engine cc, litres and horsepower: what the numbers meanConvert engine size between cc, litres and cubic inches exactly, see why horsepower can only be estimated from engine size, and decode hp, bhp, PS and kW.
- How to schedule a meeting across time zones without mistakesFind hours that suit people in several countries, avoid the daylight saving weeks that move meetings, and write invites nobody can misread.
- How to count the days between two datesCount days, weeks and months between two dates, decide whether to include the end date, and avoid the month-length and leap-year mistakes of counting by hand.
- What is a healthy weight for my height?The healthy weight range for your height in kilograms and pounds, how it is worked out from BMI, and why it is a range rather than a single ideal number.
- BMI cut-offs for Asian adults: why 23 mattersFor people of South Asian, Chinese and other Asian backgrounds, health risks rise at a lower BMI. The 23 and 27.5 cut-offs, their origin and how to use them.
- Fever temperatures in Celsius and FahrenheitIs 37.8 °C a fever? What is 101 °F in Celsius? A body temperature conversion chart, where a fever starts, and how the thermometer site changes the reading.
- Knots to mph and km/h: how fast is a knot?One knot is one nautical mile per hour: 1.852 km/h or about 1.15 mph. A conversion table for boats, planes and wind, and why sailors and pilots still use knots.
- How to convert mpg to litres per 100 km (and back)Convert fuel economy between US mpg, UK mpg, litres per 100 km and km per litre, with tables, formulas, and why US and UK figures differ for the same car.
- Mbps vs MB/s: how fast will my download really be?A 100 Mbps connection downloads at about 12.5 megabytes per second, not 100. Bits versus bytes, download time tables, and why real speeds come in a little lower.
- How to measure a room in square feet and square metresMeasure a room's floor area, convert between square feet and square metres, handle L-shaped rooms, and add the right allowance when buying flooring.
- How many rolls of wallpaper do I need?Count wallpaper the way decorators do: by drops, not by area. A worked example, how pattern repeat changes the answer, and why to buy from one batch.
- EST vs EDT, GMT vs UTC: time zone abbreviations explainedEST is not the same as EDT, and GMT is not quite UTC. What common time zone abbreviations mean, when daylight saving changes them, and how to avoid missed calls.
- How to convert minutes to decimal hours for timesheets7 hours 45 minutes is 7.75 hours, not 7.45. A minutes-to-decimal table, the formula, and how to avoid the most common timesheet and invoicing mistake.
- How to invoice a client in another currencyWhich currency to bill in, how to show it so nobody is confused, who pays bank and conversion fees, and what to record for tax when you invoice clients abroad.
- ISO 8601 date format explained (YYYY-MM-DD and beyond)2026-10-03T14:30:00Z decoded: the international date and time format, time zones and offsets, week numbers and durations, and why it is the safest format to use.
- Celsius to Fahrenheit in your head: the shortcut and where it fails“Double it and add 30” is close for weather but wrong for fevers and ovens. How accurate it is, a better mental method, and reference points to remember.
- Square metres vs metres squared: area conversion mistakesWhy 1 m² is 10.76 square feet, not 3.28, why “2 metres squared” is ambiguous, and how to convert areas and volumes without the most common mistakes.
- Stones and pounds to kg: why 11.5 stone isn’t 11 st 5 lbA stone is 14 pounds, so decimal stones and stones-and-pounds are not the same. How to convert st and lb to kg and back, with worked examples and a quick check.
- Ton vs tonne: metric, short and long tons explainedA tonne is 1,000 kg, a US short ton 907 kg, and a UK long ton 1,016 kg. Which one a document means, why air conditioners are rated in tons, and how to convert.
- US vs UK pints, gallons and fluid ounces: why they differA UK pint is 568 ml, a US pint 473 ml. The UK fluid ounce is smaller, but there are 20 in a UK pint. The differences, why they exist and how to avoid mix-ups.
- Kilometres to miles in your head: three quick methodsMultiply by 5 and divide by 8, use the Fibonacci trick, or take 60%. How accurate each mental method is for distances and speeds, with worked examples.
- Troy ounce vs ounce: why gold is weighed differentlyGold and silver prices are per troy ounce, 31.1 g, not the 28.35 g ounce on kitchen scales. How to convert troy ounces to grams and check what a price means.
- kW vs kWh: the difference, and why your bill uses kWhkW is how fast energy is used; kWh is how much is used. How to turn appliance power into energy and cost, and how EV battery and charger figures fit together.