Lessons · Medicine foundations · pounds to kilograms, feet and inches to centimetres
Pounds to kilograms, feet and inches to centimetres
Almost every formula in this track wants kilograms and centimetres, so the first line of the working is usually just the conversion.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
The chart says 154 lb and 5 ft 9 in. The formula on the whiteboard wants kg and cm. On a first-year paper, most of the wrong answers are not bad arithmetic; they are good arithmetic done on the wrong units, and the marker cannot tell the difference from the number alone.
How to think about it
Convert on its own line, before the formula is touched, and keep the unit attached. Pounds divided by the factor the problem gives is kilograms. Feet times 12, plus the inches, is total inches; total inches times 2.54 is centimetres; centimetres over 100 is metres.
Worked example
154 / 2.2 = 70 kgThe problem gave 2.2 pounds to the kilogram. A person is a smaller count of kilograms than of pounds, which is the sense check.
5 ft 9 in = 5 × 12 + 9 = 69 inEverything into inches first. Sixty-nine of them.
69 × 2.54 = 175.26 cmThe problem gave 2.54 centimetres to the inch.
175.26 cm = 1.7526 mAnd metres when a formula asks for metres. One hundred centimetres to the metre.
Your turn
A chart gives a weight of 187 lb, and the problem gives 2.2 pounds to the kilogram. Write the line that gives the weight in kilograms.
187 / 2.2 = kg
Solve one, graded on the server
The trap
Multiplying by 2.2 instead of dividing, which turns a 187 lb adult into 411 kg. Say the sentence out loud before you write it: one kilogram is more than one pound, so there are fewer kilograms in the answer than pounds in the question.