US Measurement Units: Fahrenheit, Miles and Pounds Explained
The US doesn't use the metric system, and that changes how you read weather, weight, and distance.
In short: The US is one of the few countries that doesn't use the metric system in daily life, so you'll deal with Fahrenheit instead of Celsius, miles instead of kilometers, pounds instead of kilograms, gallons instead of liters, and inches instead of centimeters. Quick reference: 70°F is a mild, pleasant day, 90°F is seriously hot, and 32°F is the exact freezing point of water. For a precise number, use the unit converter tool instead of doing it by hand.
Why doesn't the US use the metric system?
Most of the world, including every Arab country, uses the metric system (meters, kilograms, liters, Celsius). The US is one of the few major exceptions worldwide that still runs on the Imperial/US Customary system in daily life: Fahrenheit for temperature, miles for distance, pounds for weight, gallons for liquids, and inches and feet for length. That doesn't mean metric is absent entirely — hospitals, scientific labs, professional sports (like the 100-meter dash), and some food packaging list metric weights too.
You don't need to memorize complicated formulas, just a handful of reference points that cover most everyday situations: weather, cooking, driving, and clothing.
Temperature: how do you read Fahrenheit quickly?
The precise formula is: Fahrenheit = (Celsius × 9/5) + 32. In daily use, though, these reference points are faster than calculating each time:
| Fahrenheit | Approx. Celsius | What it feels like |
|---|---|---|
| 32°F | 0°C | Water's exact freezing point, roads may ice up |
| 50°F | 10°C | Cool, jacket weather |
| 70°F | 21°C | Mild and pleasant |
| 90°F | 32°C | Seriously hot |
| 98.6°F | 37°C | Normal human body temperature |
| 212°F | 100°C | Water's exact boiling point |
A quick mental shortcut: subtract 30 from the Fahrenheit number, then divide by 2, for a rough (not exact) Celsius estimate. Example: 80°F, minus 30 = 50, divided by 2 = about 25°C (the precise figure is 26.7°C).
Distance: miles vs. kilometers
One mile equals about 1.609 kilometers, meaning a kilometer is shorter than a mile. For a quick estimate: multiply miles by 1.6 to get approximate kilometers, or multiply kilometers by 0.62 to get approximate miles.
| Context | US units | Approx. equivalent |
|---|---|---|
| Standard highway speed | 65–70 mph | 105–113 km/h |
| Common city driving speed | 25–35 mph | 40–56 km/h |
| Medium distance between two nearby cities | 50 miles | about 80 km |
Speed limit signs on US roads are always in miles, never kilometers, so make sure your car's speedometer reads "MPH" if it's an import. See the driver's license guide before your first driving test in the US.
Small lengths: inches and feet
One inch equals about 2.54 centimeters, and one foot equals 12 inches, or about 30.5 centimeters. Human height and apartment or furniture descriptions are usually given in feet and inches together, like "5 feet 7 inches" to describe someone's height, not centimeters as you might be used to.
Weight: pounds vs. kilograms
One pound (lb) equals about 0.454 kilograms, meaning a kilogram is more than double a pound. For a quick estimate: divide the number of pounds by 2.2 to get approximate kilograms.
| In pounds | Approx. equivalent in kg |
|---|---|
| 1 lb | 0.45 kg |
| 10 lb | 4.5 kg |
| 100 lb | 45.4 kg |
| 150 lb | 68 kg |
Scales at US pharmacies and hospitals usually display weight in pounds, though some medical facilities show kilograms alongside it. Ask the nurse or doctor to give you the number in kilograms if that's more comfortable for you.
Liquids: gallons and cups in cooking and fuel
The most common liquid unit is the gallon, used for selling fuel and milk in larger quantities. A US gallon equals about 3.785 liters (note: the UK gallon is different and somewhat larger — don't confuse the two).
| US unit | Approx. equivalent |
|---|---|
| 1 gallon | 3.785 liters |
| 1 cup | about 237 ml |
| 1 tablespoon | about 15 ml |
| 1 teaspoon | about 5 ml |
| 1 fluid ounce (fl oz) | about 30 ml |
American recipes measure by the "cup" as the basic unit for flour, sugar, and liquids, not grams or milliliters. If your favorite recipe is in grams, you'll need either a digital kitchen scale that converts automatically, or a dedicated set of US measuring cups, sold at any home goods store.
Clothing sizes: approximate, not an exact match
US clothing sizes (Small, Medium, Large, or numbers like 6, 8, 10 for women) don't match Arab or European sizes exactly, and they also vary between brands within the US itself. Treat any size conversion chart as a rough starting point only, and try the item on or check the specific store's own size chart before buying, especially when shopping online.
Living space: square feet, not square meters
When searching for an apartment or house to rent or buy, you'll find the size listed in square feet, not square meters as in most Arab countries. One square foot equals about 0.093 square meters, so an apartment listed at 800 square feet is roughly 74 square meters. For a quick conversion, multiply square feet by 0.093, or divide by about 10.76 to get approximate square meters.
Larger plots of land, like building lots or farmland, are sometimes measured in acres. One acre equals about 4,047 square meters — different from the "feddan" used in Egypt (about 4,200 square meters), so don't assume they're identical.
Tire pressure and paper size: small details that matter
US car tire pressure is measured in PSI (pounds per square inch), not bar as is common in some Arab countries. A typical passenger car's recommended pressure runs roughly 30 to 35 PSI, and the exact number is usually on a sticker inside the driver's door, not necessarily on the tire itself. One bar equals about 14.5 PSI.
The standard US office paper size is called "Letter," measuring 8.5 by 11 inches — different from the A4 size common worldwide and in Arab countries. If you're printing official documents or a job application, make sure your printer is set to "Letter," not "A4," so part of the page doesn't get cut off.
Common mistakes with US units
- Mixing up US and UK gallons: the difference is real, not approximate, so confirm which system a source is using.
- Estimating driving speed from kilometer instinct: driving "65" thinking it's kilometers when it's actually miles can mean speeding or driving well under the flow of traffic.
- Treating quick mental conversions as 100% exact: most rules of thumb (like the Fahrenheit or pound shortcuts) are approximate — don't use them for precise medical or engineering calculations.
- Assuming a clothing size is a fixed global number: a "Medium" at one US store can run a different size than a "Medium" at another.
What to do next
Keep this conversion table as a quick reference, and use the unit converter tool whenever you need an exact number, especially for cooking or following a medical dosage. For more practical everyday-life details in the US, see the first 90 days in the USA guide.
Frequently asked questions
What does 70°F equal in Celsius?
About 21°C, a mild and pleasant temperature.
Is a US gallon the same as a UK gallon?
No, a US gallon (3.785 liters) is smaller than a UK gallon, so confirm which system a source is using.
How do I quickly convert my weight from pounds to kilograms?
Divide the number of pounds by 2.2 for a rough estimate in kilograms.
Are US road speed signs in kilometers or miles?
Always miles, so make sure your car's speedometer reads MPH, not km/h.
How do I cook a US recipe written in cups instead of grams?
Use dedicated US measuring cups, or a digital scale that converts between cups and grams automatically.
Is a Medium clothing size the same at every US store?
No, it varies by brand, so check each store's own size chart before buying.