Unit Converter

Traveling between the United States and countries that use the metric system means constantly translating miles into kilometers, pounds into kilograms, gallons into liters, and Fahrenheit into Celsius. A unit converter built for everyday U.S. customary and SI metric pairs saves mental arithmetic and reduces costly mistakes in recipes, fitness logs, fuel planning, and real-estate comparisons.

The Yaya Tools US unit converter is a free US unit converter that runs entirely in your browser. Pick a category—length, weight, temperature, volume, area, or speed—enter a value, choose source and target units, and read the converted result instantly. No account, no upload: every calculation stays on your device. Whether you need miles to km for a road trip, pounds to kg for a health app, or fahrenheit to celsius for weather abroad, this page handles the math with transparent formulas you can verify by hand.

What is a US unit converter?

A US unit converter (also called an imperial–metric converter or customary unit calculator) translates measurements between U.S. customary units and their international metric counterparts. Unlike a generic scientific converter that lists hundreds of obscure units, this tool focuses on the pairs Americans encounter most: miles and kilometers, feet and meters, pounds and kilograms, gallons and liters, square feet and square meters, and miles per hour versus kilometers per hour.

People reach for a unit converter when they need to:

• Read a European speed limit sign while driving a U.S. rental car
• Enter body weight in kilograms for a BMI or fitness app after weighing in pounds
• Scale a recipe that lists cups and fluid ounces when your kitchen scale reads grams
• Compare home listings quoted in square feet against metric floor plans
• Estimate fuel consumption after reading distance in kilometers but paying by the gallon

Yaya Tools organizes conversions into six practical categories. Non-temperature units share one multiplication pattern; temperature uses the standard linear formulas for Fahrenheit, Celsius, and Kelvin. Results update as you type, and a swap button flips source and target units without re-entering numbers.

Privacy note: values are processed only in your local browser. Yaya Tools does not receive your inputs for server-side conversion on this tool.

How to use this unit converter

Follow these steps on the US unit converter page:

1. Choose a unit category — length, weight, temperature, volume, area, or speed.
2. Enter a numeric value — any positive or negative decimal the field accepts.
3. Select the source unit — for example, mile, pound, or fahrenheit.
4. Select the target unit — for example, kilometer, kilogram, or celsius.
5. Read the result — the converted value, original input, and conversion ratio (non-temperature categories) update automatically.
6. Optional: click the swap control — exchange source and target units to reverse the direction (miles → km becomes km → miles).

The default example converts 1 mile to kilometers. Change any field and the output refreshes immediately—there is no separate Calculate button.

Quick tip: before entering trip distance into the gas cost calculator, convert kilometers to miles here so MPG math stays consistent. After converting weight to kilograms, you can paste the result into the BMI calculator if your scale only displays pounds.

Unit converter formulas

The Yaya Tools US unit converter uses two conversion strategies, matching the live implementation.

Non-temperature units: factor ratio

For length, weight, volume, area, and speed, each unit stores a factor relative to a base unit in that category (meters, kilograms, liters, square meters, or meters per second). The conversion formula is:

result = value × fromFactor ÷ toFactor

The displayed conversion ratio is fromFactor ÷ toFactor for the selected pair. Example: converting miles to kilometers uses factors 1609.344 (mile) and 1000 (kilometer):

result = value × 1609.344 ÷ 1000

One mile therefore equals 1.609344 kilometers—a figure you will see on U.S. highway signs that list both units on some border routes.

Temperature: standard linear formulas

Temperature does not use simple multipliers because the Fahrenheit and Celsius scales have different zero points. The tool first converts any input to Celsius, then converts Celsius to the target scale:

To Celsius (intermediate step)

°C = (°F − 32) × 5 ÷ 9        when converting from Fahrenheit
°C = K − 273.15               when converting from Kelvin
°C = input                    when input is already Celsius

From Celsius to target

°F = °C × 9 ÷ 5 + 32          when target is Fahrenheit
K  = °C + 273.15              when target is Kelvin
output = °C                   when target is Celsius

These are the same fahrenheit to celsius and celsius to fahrenheit formulas taught in science classes worldwide. Kelvin is included for academic and engineering contexts where absolute temperature matters.

Length: mile, kilometer, foot, meter, inch

Length conversions bridge U.S. road signs, construction plans, and sports measurements with metric standards used in most other countries.

Miles to km is the most searched length pair. Multiply miles by 1.609344, or use the tool: 10 miles → 16.09344 km. For shorter distances, 1 foot = 0.3048 m and 1 inch = 2.54 cm (0.0254 m exactly by international definition).

When budgeting fuel for a trip measured in kilometers, convert to miles first, then open the gas cost calculator with MPG and USD per gallon—mixing km with MPG silently breaks gallon estimates.

Weight: pound, ounce, kilogram, gram

U.S. bathroom scales and gym weights typically read pounds and ounces. Medical and international fitness apps often expect kilograms.

Pounds to kg: multiply pounds by 0.45359237. Example: 150 lb → 68.0388555 kg. For the BMI calculator, enter height in centimeters and weight in kilograms—convert here if your scale shows pounds only.

Remember that ounces in this weight category are avoirdupois ounces, not fluid ounces. Volume ounces measure liquid capacity and belong in the volume category.

Temperature: Fahrenheit, Celsius, Kelvin

Weather reports, oven settings, and medical thermometers may use different scales. The fahrenheit to celsius conversion most travelers need is:

°C = (°F − 32) × 5 ÷ 9

Example: 68 °F (mild spring day) → 20 °C. Freezing water is 32 °F or 0 °C; boiling at sea level is 212 °F or 100 °C.

Reverse (celsius to fahrenheit):

°F = °C × 9 ÷ 5 + 32

Kelvin adds 273.15 to Celsius for absolute temperature: 0 K is absolute zero. Room temperature (~20 °C) is about 293.15 K. The converter handles all three pairs without approximating temperature as a simple multiplier.

Volume: gallon, quart, cup, liter, fluid ounce

U.S. liquid cooking and fuel volumes differ from metric liters. This tool uses U.S. customary liquid definitions (not the smaller U.S. dry gallon, and not the larger British imperial gallon).

One gallon equals 3.785411784 liters—useful when comparing European fuel economy (L/100 km) with U.S. MPG. Cup-to-liter scaling helps adapt baking recipes; note that ingredient mass still depends on density (a cup of flour weighs less than a cup of honey).

Area: square foot, square meter, acre

Real estate, flooring, and land listings mix square feet with acres and, internationally, square meters.

A 2,000 ft² home is about 185.8 m². One acre is roughly 4,047 m² or 0.4047 hectare—handy when comparing suburban U.S. lots to metric plot sizes abroad.

Speed: mph, km/h, m/s

Speed limits, vehicle specs, and physics problems use different speed units.

Miles to km at constant speed: 60 mph ≈ 96.56 km/h. The factors derive from length conversions (1 mile = 1609.344 m, 1 hour = 3600 s). Enter your speed in mph when comparing rental-car limits overseas.

Worked examples

These examples match the on-page formulas; you can reproduce each in the live tool.

Example 1: Miles to km for a 350-mile drive

350 × 1609.344 ÷ 1000 = 563.2704 km

A 350-mile one-way trip is about 563 km. Paste 350 (miles) into the gas cost calculator if your car’s MPG is U.S.-style.

Example 2: Pounds to kg for BMI entry

A scale reads 180 lb:

180 × 0.45359237 ÷ 1 = 81.6466266 kg

Enter 170 cm and 81.6 kg (rounded) in the BMI calculator for a screening estimate. Categories on that page use Chinese adult cutoffs—interpret alongside your health context.

Example 3: Fahrenheit to Celsius for travel weather

Forecast shows 95 °F:

°C = (95 − 32) × 5 ÷ 9 = 35 °C

That is a hot summer day—roughly body temperature in Celsius terms, which helps calibrate expectations when packing.

Example 4: Gallons to liters at the pump

You need 12 gallons for a generator:

12 × 3.785411784 ÷ 1 = 45.424941408 L

Compare that to a 40 L portable tank before buying.

Example 5: Square feet to square meters for an apartment

Listing shows 850 ft²:

850 × 0.09290304 ÷ 1 = 78.967584 m²

Use the figure to compare with European listings quoted in m².

Example 6: mph to km/h on the highway

Cruise control set to 65 mph:

65 × 0.44704 ÷ 0.2777777778 ≈ 104.607 km/h

Many Canadian and European highways post limits in km/h near that range.

Common mistakes when converting units

Mixing weight ounces with fluid ounces. Sixteen fluid ounces of water occupy about one pint, but sixteen weight ounces equal one pound. Use the weight category for pounds and ounces on a scale; use volume for cups and fl oz in recipes.

Using the wrong gallon. U.S. liquid gallons differ from imperial gallons used in the UK. This US unit converter applies U.S. liquid definitions (3.785 L per gallon).

Assuming temperature doubles like length. 40 °F is not “twice as hot” as 20 °F in Celsius—the scales offset at different zero points. Always use the Fahrenheit/Celsius formulas, not a ratio.

Converting then mixing units in downstream tools. MPG requires miles; BMI on Yaya Tools expects kilograms and centimeters. Convert once here, then enter consistent units in the gas cost calculator or BMI calculator.

Rounding too early in chains. Converting 10 miles → km → back to miles accumulates error if you round each step. Keep full precision in the tool and round only for display.

Ignoring sign or negative temperatures. Valid negative Celsius and Fahrenheit values convert correctly (for example, −40 °F = −40 °C). Enter them as signed numbers when needed.

Expecting cup weight from cup volume. Two cups of flour and two cups of sugar have different masses. Volume conversion tells you liquid capacity, not grams—unless you know density.

Related tools for travel, health, and money math

Unit conversion is often the first step before another calculator:

• Gas cost calculator — estimate trip fuel cost from miles, MPG, and USD per gallon after converting km → miles here.
• BMI calculator — compute body mass index from height (cm) and weight (kg) after pounds to kg conversion.
• Percentage calculator — express how much a converted value changed versus an original (for example, a 10% lighter luggage limit in kg compared to your lb baseline).

Together, these tools cover common U.S.–metric workflows without leaving Yaya Tools.

Sources and methodology

The conversion constants are based on the NIST Guide to the SI, Appendix B, including the exact international foot (0.3048 m), yard (0.9144 m), and mile (1,609.344 m). NIST also documents the distinction between the international foot and the retired U.S. survey foot; this everyday converter uses the international definitions, not legacy survey units.

Temperature conversion is an affine formula rather than a simple multiplication, and volume entries distinguish U.S. customary units from similarly named imperial units. Results are rounded for display and are not intended for metrology, calibration, surveying, or regulated trade measurements.