Unit Converter

Convert between thousands of units instantly across length, weight, temperature, speed, area, volume, time, digital storage, engineering, science, cooking, finance, and more.

Thermal Conductivity

W/(m·K), BTU/(h·ft·°F)

From

Result

0.00239

1 W/(m·K) = 0.00239006 cal/(s·cm·K)

Popular conversions

What is a Unit Converter?

A unit converter turns a value in one unit of measurement into the equivalent value in another — the same physical quantity expressed on a different scale. Under the hood almost every conversion is a multiplication by a fixed, internationally-agreed factor; the only common exception is temperature, which uses an offset because the scales don't share a zero point.

SamCalculator's Unit Converter rolls forty-plus categories into a single workspace — distance, area, volume, weight, temperature, time, speed, pressure, energy, power, force, torque, frequency, angle, density, fuel economy, electrical quantities, light, radiation, digital storage, data transfer, cooking, astronomy, nautical, construction, medical dosage, currency, and crypto. Pair it with our percentage calculator, scientific calculator, BMI calculator, and discount calculator for the matching everyday maths.

How Unit Conversion Works

One factor per unit

Every unit is stored as a multiplier against a category base — metres for length, kilograms for mass, seconds for time, pascals for pressure. To convert A → B the tool multiplies by A's factor (taking the value into the base) and divides by B's factor.

Temperature is the offset case

Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur don't share a zero. The converter uses the exact algebraic formulas — °F = °C × 9⁄5 + 32 and friends — instead of a plain multiplication.

Live data for currency and crypto

Currency rates load from the open.er-api.com USD-base feed on every visit; crypto prices come from CoinGecko. When a live feed is unreachable, a clearly-labelled indicative table dated 2026-05-25 takes over.

Precision is bounded only by IEEE-754

Maths runs in JavaScript double precision — about 15 significant digits. The precision slider lets you display 0 to 12 decimal places, and the notation toggle switches between plain, scientific, and engineering output.

Six Ways to Use This Converter

Travel & Distance

Switch between miles and kilometres, feet and metres, gallons and litres for road trips, packing weight limits, and overseas recipes.

Kitchen & Recipes

Convert cups, tablespoons, fluid ounces, and metric millilitres — including US vs UK vs Australian cup sizes that recipes rarely label.

Engineering & Lab

Pa, bar, atm, psi for pressure. N, lbf, kgf for force. J, BTU, kWh for energy. Switch notation to Engineering for groups-of-three exponents.

Tech & Storage

GB vs GiB, Mbps vs MB/s, ppi vs ppcm — the kind of conversions every drive and bandwidth quote forces you to do, in one place.

Money & Crypto

Live USD-base currency rates across 160+ currencies, plus 20+ major cryptocurrencies — handy for travel, freelancing, and quick price checks.

Health & Construction

mg/kg drug dosing, mmol/L vs mg/dL blood glucose, cement-bag volumes, wheelbarrow loads — the niche categories most converters skip.

Best Conversion Practices

Get into the habit of writing units next to every number you handle. The single biggest source of conversion mistakes — in homework, in spreadsheets, in engineering documents — is a number stripped of its unit and reused later as if it were on a different scale. Treat "5" as incomplete; treat "5 kg" or "5 lb" as a value.

Three habits stop nearly every real-world conversion bug. First, always check the system: US Customary, UK Imperial, and metric look similar but disagree on fluid ounces, gallons, and tons. Second, watch out for SI-vs-binary prefixes in digital storage — GB and GiB are not the same, and a 1 TB drive really is 1,000,000,000,000 bytes. Third, when temperature is involved, never multiply — the offset means °C × 2 ≠ 2× °F.

For high-stakes work — medical dosing, structural calculations, aerospace, finance — convert and then sanity-check. The Mars Climate Orbiter, the Gimli Glider, and several drug-overdose investigations all trace back to unit conversions that the team failed to verify with a second calculation. Treat conversion as a two-step process: compute, then validate the order of magnitude.

Why Accurate Conversion Matters

Mars Climate Orbiter (1999)

NASA lost a $327 million spacecraft because one team specified thrust in pound-seconds while another expected newton-seconds. A factor-of-4.45 error pushed the orbiter into the Martian atmosphere instead of orbit. A single conversion check would have caught it.

Gimli Glider (1983)

Air Canada Flight 143 ran out of fuel mid-flight after ground crew loaded litres instead of kilograms — a 2.2× shortfall. The pilots glided the 767 to a safe landing on an abandoned runway. The crash investigation found a metric-imperial conversion error in the fuelling sheet.

Medical dosing

Drug labels in the US default to mg/kg of body weight, but patient weights are recorded in either pounds or kilograms depending on the hospital. A confused converter can give a 2.2× overdose to a child. Clinical guidelines now require explicit unit confirmation on every prescription.

Construction and trade

Imported equipment specs in N·m torque are routinely misread as lb·ft (a 1.36× factor). Plumbing pipes labelled in DN (millimetres) vs NPS (nominal inches) cause connection mismatches. Always check both the unit label and the target system.

Metric vs Imperial — and Why Both Still Exist

The metric system — officially the International System of Units (SI) — was designed in 1790s France to be coherent, decimal, and universal. Since 2019 every SI base unit (metre, kilogram, second, ampere, kelvin, mole, candela) is anchored to a fundamental physical constant rather than a physical artifact, which makes SI reproducible in any well-equipped lab on Earth.

Imperial and US Customary units (inch, foot, mile, pound, gallon, fluid ounce) descend from medieval English standards that varied between trades and regions. The US, Liberia, and Myanmar are the only countries that haven't officially adopted SI as the legal measurement system — but even those holdouts use SI for science, medicine, and international trade. The UK is the most interesting hybrid: distances on road signs are in miles, beer is sold in pints, but goods are weighed in kilograms and temperatures are reported in Celsius. Aviation worldwide kept feet for altitude and nautical miles for distance for international compatibility.

Where Conversions Get Tricky

US vs UK fluid ounces

A US fl oz is 29.5735 mL; a UK (Imperial) fl oz is 28.4131 mL — about 4% smaller. UK pints (568.26 mL) are 20% larger than US pints (473.18 mL). British recipes scaled by US measuring cups are always slightly off.

Cups around the world

US cup: 236.588 mL. Metric cup: 250 mL. UK cup: 284.131 mL. Japanese cup: 200 mL. If a recipe doesn't specify the system, assume the country it was published in.

GB vs GiB (storage)

Hard-drive marketing uses powers of 10 (1 TB = 10¹² bytes); operating systems use powers of 2 (1 TiB = 2⁴⁰ bytes). A "1 TB" drive shows up as 931 GB on the desktop — nothing's missing, just different prefixes.

Short ton, long ton, metric ton

1 short ton (US) = 907.185 kg; 1 long ton (UK) = 1,016.047 kg; 1 metric ton (tonne) = 1,000 kg. Shipping invoices that just say "ton" can be off by 10% — always verify the system.

The Core Conversion Formulas

Every result this converter produces boils down to a small set of exact equations. Memorising even a handful lets you sanity-check any conversion you read on a label or in a spec sheet.

Linear conversion

B = A × (factor_A / factor_B)

The general rule for any multiplicative conversion: multiply by source factor, divide by target factor — both relative to the category base.

Celsius to Fahrenheit

°F = °C × 9/5 + 32

Temperature is the offset case. The 9/5 handles the degree size, the +32 handles the differing zero points (water freezes at 0 °C / 32 °F).

Real-purchasing currency

Local = USD × rate_local

Currency uses live USD-base rates from open.er-api.com. Mid-market rate; retail bank rates are typically 2-4% wider plus a fixed fee.

Common Conversion Mistakes

1
Dropping the unit
The single biggest source of conversion bugs is writing down a bare number and re-using it later as if it were on a different scale. Always carry the unit through every cell of a spreadsheet and every line of an equation.
2
Multiplying temperature
20 °C is not twice 10 °C — the zero point isn't physical zero. Whenever temperature appears, use the algebraic conversion (°F = °C × 9⁄5 + 32, K = °C + 273.15), never a bare multiplier.
3
Confusing SI and binary prefixes
kB ≠ KiB, MB ≠ MiB, GB ≠ GiB. The difference grows with scale — a 1 TB drive is 7.4% smaller than a 1 TiB allocation. Always check whether the source is using SI (10ⁿ) or binary (2ⁿ) prefixes.
4
Assuming "ton" means metric
Short ton (US) = 907.185 kg. Long ton (UK) = 1,016.047 kg. Metric ton = 1,000 kg. Shipping invoices and material specs that just say "ton" can be off by up to 10% — always confirm.
5
Mixing US and UK fluid units
US fluid ounce, gallon, pint, and quart are 17-20% smaller than their UK Imperial counterparts. A British pudding recipe scaled by American measuring cups will always disappoint.

Built for students, engineers, cooks, travellers, and anyone who lives between unit systems.

Linear unit factors follow the BIPM SI brochure, the NIST Guide to the SI, and ISO 80000. Temperature, fuel economy, and pixel-density use closed-form algebraic equations. Currency rates load live from open.er-api.com (USD base); crypto prices from CoinGecko. See our methodology and editorial policy. Educational only — not certified for regulated trading, settlement, or aerospace use.

Frequently Asked Questions

A unit converter is a small online utility that takes a value you have in one unit (say, 100 dollars, 5 kilograms, or 60 miles per hour) and gives you the same physical quantity in a different unit (Euros, pounds, or kilometres per hour). SamCalculator's Unit Converter rolls that idea into a single workspace covering more than forty categories — distance, area, volume, weight, temperature, speed, pressure, energy, power, force, torque, frequency, angle, density, fuel economy, electrical quantities, light, radiation, digital storage, data transfer, typography, cooking, astronomy, nautical, construction, medical dosage, currency, crypto, and more. The answer updates as you type, and you can swap, copy, share, print, or favourite any conversion in one tap.

For nearly every unit the converter stores a single multiplicative factor that maps it to a category-specific base unit — metres for length, kilograms for mass, seconds for time, pascals for pressure, and so on. To go from unit A to unit B it first multiplies your value by A's factor (taking it into the base unit) and then divides by B's factor. Temperature is the odd one out because the scales don't share a zero, so it uses the proper algebraic formulas instead. Fuel economy uses a reciprocal because miles per gallon and litres per 100 km are inversely related. The maths runs in your browser at IEEE-754 double precision, which is roughly 15 significant decimal digits — far more than any practical conversion needs.

Almost. The metric system — officially the International System of Units (SI) — is the legal measurement system in every country except the United States, Liberia, and Myanmar. Even those holdouts use SI for science, medicine, and most international trade; imperial units stick around in retail, cooking, weather, and road signage. The UK is a fascinating hybrid: distances on road signs are in miles, beer is sold in pints, but goods are weighed in kilograms and temperatures are reported in Celsius. Aviation is metric for almost everything except altitude (feet) and horizontal distance (nautical miles), which stayed imperial for international compatibility.

SI has seven base units that everything else is built from: the metre (length), kilogram (mass), second (time), ampere (electric current), kelvin (temperature), mole (amount of substance), and candela (luminous intensity). Every other unit you've heard of — newton, joule, watt, pascal, volt, ohm, tesla, lux — is a derived unit, just a named combination of the seven. A newton, for example, is one kilogram-metre per second squared. Since 2019 every base unit is anchored to a fundamental physical constant rather than a physical artifact, which means SI values can be reproduced in any well-equipped lab without a reference object.

Fahrenheit to Celsius is °C = (°F − 32) × 5⁄9. Celsius to Fahrenheit is °F = °C × 9⁄5 + 32. The −32 (or +32) handles the offset between the two zero points; the 5⁄9 (or 9⁄5) handles the difference in degree size. A quick mental shortcut: double the Celsius value and add 30 to get a rough Fahrenheit (25 °C → ~80 °F, actual 77 °F). For everyday weather that gets you within a couple of degrees, which is usually close enough. The converter on this page handles the exact maths plus Kelvin, Rankine, and Réaumur too.

Drive manufacturers count storage in powers of ten: 1 TB literally means 1,000,000,000,000 bytes. Operating systems count in powers of two: 1 TiB is 2⁴⁰ bytes, which is about 9.95% more. Microsoft Windows historically displays GB but uses GiB maths, so a brand-new 1 TB drive shows up as roughly 931 GB on the desktop even though nothing is missing. The Digital Storage category on this page exposes both SI prefixes (kB, MB, GB, TB) and binary prefixes (KiB, MiB, GiB, TiB) so you can confirm a drive's real capacity at a glance.

As accurate as the published conversion factors themselves. Every linear factor here is the exact internationally-agreed value — 1 inch is 2.54 cm, 1 pound is 0.45359237 kg, 1 BTU is 1,055.05585262 J, and so on. Temperatures use the closed-form algebraic equations rather than approximations. The maths runs in JavaScript's double-precision floating point, which is accurate to about 15 significant decimal digits — well beyond the precision any kitchen, gym, workshop, or finance use will ever need. You can dial the displayed precision anywhere from 0 to 12 decimal places.

Yes. The full category list includes pressure (Pa, bar, atm, psi, mmHg, inHg, torr, kgf/cm²), force (N, lbf, kgf, dyne, poundal), torque (N·m, lb·ft, lb·in, oz·in, kgf·m), energy (J, kJ, MJ, kcal, kWh, BTU, eV, ft·lb, therm), power (W, kW, MW, hp, BTU/h, ton of refrigeration), density, flow rate, fuel economy, electrical current / voltage / resistance / capacitance / conductance, magnetic field, illuminance, luminance, thermal conductivity, heat flux, and radiation dose. Switch the notation toggle to Engineering to render results in groups of three exponents the way scientific papers and lab reports do.

Currency rates load on every visit from the open.er-api.com free API, which republishes the daily USD-base mid-market quotes from major banking data providers. Crypto prices come from CoinGecko's public price endpoint and cover 20+ of the most-traded coins. Both are aimed at giving you a near-real-time picture for conversion and quick reference — they're not a settlement-grade feed, so for an actual money transfer or trade you should use your bank or broker's live quote. If either feed is unreachable, a clearly-labelled fallback table dated 2026-05-25 is shown so the converter never silently misleads you.

No. All conversion maths runs in your browser. Your last-used category, From / To units, recent history (up to 50 entries), and starred Favorites are stored in your browser's local storage on your own device — they aren't uploaded, aren't linked to an account, and don't leave your machine. The Currency and Crypto categories fetch live rate tables from open.er-api.com and CoinGecko respectively, but those requests don't carry any of your conversion content. Close the tab and the entire session is over.