What the IN function does and when you need it
The IN function converts a number from one unit of measurement to another — inches to centimeters, pounds to kilograms, gallons to liters, and so on. Most scientific and graphing calculators have this function built in, though the exact name and location varies by model. If you are measuring something in one unit but need the answer in another, IN (or a similar conversion function) saves you from looking up the conversion rate and doing the math by hand.
The function works the same way on nearly every calculator: you enter a number, press the conversion button, choose which units you are converting between, and the calculator does the rest. The speed matters most when you are converting many measurements in a row — for a single conversion, looking it up online takes about the same time, but for five or ten conversions, using the calculator function is noticeably faster.
Key Takeaways
- The IN function converts measurements between units; you enter the number, select the conversion type, and the calculator displays the result.
- Different calculator brands place the conversion function in different menus — check your manual or look for a button labeled CONV, UNIT, or MODE.
- You must enter the number first, then press the conversion button, then choose the units — doing it in the wrong order will give you an error or the wrong answer.
- Common conversions include length (inches to centimeters), weight (pounds to kilograms), and volume (gallons to liters), but the available conversions depend on your calculator model.
Finding the IN or conversion function on your calculator
The conversion function is not always labeled IN. On Texas Instruments calculators (TI-84, TI-83), it is usually under the MATH menu, then look for CONV or UNIT. On Casio calculators, it is often a dedicated button on the keypad labeled CONV or UNIT. On HP calculators, conversion is sometimes under a TOOLS or CONVERT menu. If your calculator has a manual — either printed or as a PDF on the manufacturer's website — search for "convert" or "unit" to find the exact location.
If you cannot find a dedicated conversion function, your calculator may not have one built in. Older basic calculators and some phone calculator apps do not include unit conversion. In that case, you will need to look up the conversion rate (for example, 1 inch = 2.54 centimeters) and multiply or divide by hand. Scientific calculators almost always have conversion built in, so if you use your calculator regularly for measurements, a scientific model is worth the small cost.
Step-by-step: converting a measurement
Start by entering the number you want to convert. If you are converting 15 inches to centimeters, type 15 into your calculator. Do not press equals yet.
Next, press the button or menu option that opens the conversion function. On a TI-84, this means pressing MATH, then scrolling down to CONV. On a Casio, you may press a CONV button directly. The screen will show a list of conversion categories — length, weight, temperature, volume, and so on. Select the category that matches what you are converting. For inches to centimeters, choose length or distance.
After you select the category, the calculator will show you pairs of units. You will see something like "in→cm" (inches to centimeters) or separate options for "from inches" and "to centimeters." Select the pair that matches your conversion. Once you select it, the calculator will automatically multiply or divide your original number and display the result. For 15 inches, the answer will be 38.1 centimeters.
Common conversions and what to expect
Length conversions are the most common: inches to centimeters, feet to meters, miles to kilometers. Weight conversions include pounds to kilograms and ounces to grams. Volume conversions cover gallons to liters, cups to milliliters, and fluid ounces to milliliters. Temperature conversions (Fahrenheit to Celsius) work slightly differently because they require addition or subtraction, not just multiplication, so some calculators handle them in a separate menu.
The number of conversions available depends on your calculator model. A basic scientific calculator may have 20 to 30 common conversions. A graphing calculator or advanced scientific model may have 100 or more. If you need a conversion your calculator does not have, you can still do it by hand: divide or multiply by the conversion rate. For example, to convert 5 stone to kilograms, look up that 1 stone = 6.35 kilograms, then multiply 5 × 6.35 = 31.75 kilograms.
What to do if the conversion gives you the wrong answer
The most common mistake is pressing equals before selecting the conversion. If you type 15, press equals, then try to convert, the calculator will try to convert the number 15 as if it were already in a different unit, which gives nonsense. Always enter the number, then when ready press the conversion button, before pressing equals.
The second common mistake is selecting the wrong unit pair. If you meant to convert inches to centimeters but accidentally selected inches to millimeters, your answer will be off by a factor of 10. Check the screen carefully when you are selecting the conversion type. If you make a mistake, press the clear button (usually labeled C or AC) and start over from the beginning.
Temperature conversions sometimes surprise people because the conversion is not a straightforward multiplication. If your calculator shows a temperature conversion that seems wrong, check whether it is converting Fahrenheit to Celsius or Celsius to Fahrenheit — you may have selected the pair backwards. The conversion from 32 Fahrenheit should give you 0 Celsius; if it does not, you selected the wrong direction.
When to convert on your calculator versus by hand
Use the calculator conversion function when you are converting many measurements, when you need the answer quickly, or when you are not sure of the conversion rate. Use the by-hand method when your calculator does not have the conversion built in, when you are converting something unusual that the calculator does not support, or when you want to understand how the conversion works (multiplying by the rate teaches you the relationship between the units better than pressing a button).
If you are doing a project that requires many conversions — cooking a recipe from another country, building something with measurements in a different unit system, or working through a science problem — the calculator function saves time and reduces the chance of error. If you are converting one or two measurements and you have internet access, looking up the answer online may be just as fast.
Frequently Asked Questions
Does every scientific calculator have a conversion function?
Most scientific calculators have unit conversion, but not all. Older models and very basic scientific calculators may not include it. Graphing calculators (like the TI-84) almost always have conversion. Check your manual or the manufacturer's website to confirm your model has it before you buy.
Can I convert between units that my calculator does not have?
Yes. Look up the conversion rate online, then use your calculator to multiply or divide. For example, to convert 10 stone to pounds, look up that 1 stone = 14 pounds, then calculate 10 × 14 = 140 pounds. This takes a few seconds longer than using a built-in function, but it works for any unit pair.
Why does my temperature conversion look wrong?
Temperature conversions require addition or subtraction in addition to multiplication, so they work differently from other conversions. Also, you may have selected the conversion in the wrong direction (Fahrenheit to Celsius instead of Celsius to Fahrenheit). Check your manual for how your specific calculator handles temperature, and verify you selected the correct direction.
What if I convert a number and get a very long decimal?
That is normal. Most conversions produce decimals. If you need to round the answer, use your calculator's rounding function or round by hand to the number of decimal places you need. For cooking, rounding to one decimal place is usually fine. For science or engineering, keep more decimal places.
Can I convert between metric and imperial units?
Yes, that is one of the most common uses of the conversion function. Inches to centimeters, pounds to kilograms, gallons to liters — all of these are metric-to-imperial or imperial-to-metric conversions, and they are built into most scientific calculators.