Five foot nine and 70 degrees: the units that leave you lost in English

A doctor's office in Texas. The nurse checks the scale and writes it down: "One fifty-four. And you're about five foot nine?" You nod with no idea whether that's a lot or a little. You know pound, foot, and inch, but the numbers mean nothing to you.

The problem with units in English isn't vocabulary. The numbers carry no felt sense of size, and running formulas mid-conversation won't give you one. What works is memorizing a few anchor numbers for each situation (your height, your weight, four temperatures, one speed) and the exact way they're said out loud.

The US is not "the country without the metric system"#

The United States uses the metric system, even if it doesn't look that way on the street. Elizabeth Benham, coordinator of NIST's Metric Program, puts it plainly: "It's impossible to avoid using the metric system in the United States." The foot, the pound, and the gallon are all defined in terms of the International System, and the "US, Liberia, and Myanmar" trio that circulates online is, according to NIST, a myth.

What rules daily life in the US is custom. According to a 2022 YouGov survey, 88% of Americans would give someone's height in feet and inches, and 85% would give the temperature in Fahrenheit.

A unit you don't use every day leaves your estimates with no anchor. In an experiment published in Psychological Science, Belgian and American participants estimated lengths with more uncertainty in the other country's unit: Belgians in inches, Americans in centimeters.

At the doctor's office: height, weight, and temperature#

Height is given in feet and inches: five foot nine, or just five-nine. The UK Weights and Measures Act sets the yard at 0.9144 m, so a foot is 30.48 cm and an inch is 2.54 cm: five foot nine is about 175 cm, and five-ten about 178. Merriam-Webster accepts foot as a plural next to numbers, so six feet tall and six foot tall are both correct.

Weight is given in pounds, and a pound is about 450 grams. The same UK law sets it at 0.45359237 kg: 150 pounds is about 68 kg. The CDC's adult BMI calculator asks for feet, inches, and pounds by default. Multiply your kilos by 2.2 once and keep the result.

Body temperature has one number everyone quotes, 98.6°F (37°C), but it's no longer the exact benchmark. Julie Parsonnet of Stanford, senior author of a study on declining body temperature, doesn't soften it: "What everybody grew up learning, which is that our normal temperature is 98.6, is wrong." Recognize 98.6 when you hear it, without treating it as the exact line between healthy and sick.

Can you get out "I'm five foot nine, about 150 pounds" in one go while the nurse already has her pen ready? That reflex is exactly what Tabla trains: short phrases said out loud against a time limit, until they come out without stopping to calculate.

The weather forecast in Fahrenheit#

For weather, four anchor numbers are enough: 32°F is freezing (0°C), 50°F is cool (10°C), 70°F is pleasant (21°C), and 90°F is truly hot (32°C). Forecasts talk in tens: "It'll be in the seventies" means between 21 and 26°C.

The quick rule of subtracting 30 and dividing by 2 works for weather and fails at the doctor's. It's exact at 50°F and gives 20°C for 70°F (actually 21.1). For 98.6°F it returns 34.3°C instead of 37: almost 3 degrees off, right where accuracy matters most.

A friend in Chicago tells you: "It's gonna be 50 tomorrow." Coat or swimsuit?

A jacket. 50°F is exactly 10°C, one of the four anchor numbers: cool, not beach weather. The swimsuit comes out with "in the nineties."

On the road and at the store: miles, gallons, and cups#

A mile is 1,760 yards, about 1.6 km, according to the UK Weights and Measures Act. The anchor number is that 60 mph is about 97 km/h. A speed limit is said as "sixty-five miles an hour" or just "sixty-five."

A US gallon holds 3.785 liters, according to NIST's official tables. A car that gets "30 miles per gallon" burns about 7.8 liters per 100 km. In the kitchen, a cup is 8 fluid ounces, about 237 ml, and the FDA rounds it on nutrition labels: "1 cup means 240 mL". An ounce of weight counts as 28 grams.

The British twist: stones, pints, and Celsius#

The UK mixes both systems. According to YouGov, 72% of Britons give their weight in stones and pounds, yet 72% think of temperature in Celsius and only 19% in Fahrenheit. In London, the weather forecast will feel familiar; the bathroom scale won't. Road signs give distances in miles.

A stone is 14 pounds, about 6.35 kg, according to UK law. You say "I'm eleven stone" or "eleven stone four," and 11 stone is 154 pounds, about 70 kg: the same one fifty-four the Texas nurse wrote down.

A British pint is 568 ml by law, and an American pint is about 473 ml according to NIST. Order a pint in a Manchester pub and you get 20% more than in New York.

Britain isn't drifting back to imperial. When the government consulted in 2022 on expanding imperial units, 98.7% of responses preferred metric, and the law didn't change. All that came of it was a one-pint wine bottle, which Kevin Hollinrake, the enterprise minister, introduced like this: "Innovation, freedom and choice – that's what today's announcement gives to producers and consumers alike."

You don't need to convert every number. You need a handful you know by heart, and the phrase ready to say them out loud.

Try this today: say your height and weight out loud in American format, for example "I'm five foot nine, about 150 pounds," three times in a row without touching a calculator.