spaceSpace and Physics

Bookmark This Handy Calculator For All Your Inch-Centimeter Conversions

Struggling to turn your inches into centimeters or vice-versa? Look no further!


Dr. Alfredo Carpineti


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

Alfredo (he/him) has a PhD in Astrophysics on galaxy evolution and a Master's in Quantum Fields and Fundamental Forces.

Senior Staff Writer & Space Correspondent

a white meauring tape showing both inches and centimers on a wooden table
Get your measuring tape out, we are measuring body parts! Image credit: noicherrybeans/

Even though we might not be the Vitruvian Man with its perfect proportions, it is a good habit to measure and memorize the lengths of some of your body parts – in a pinch, they can become temporary rulers when there's nothing else around to be used. Your gait, your forearm, the width of your hand, and the distance between the tip of your extended pinky and the tip of your extended thumb (think surfer dude) are all good measurements to have in mind.

And no matter where you are, it is a good idea to have those numbers in both metric and imperial units. On the internet, you'll encounter both types of units and a literal hands-on approach to how big or how small something might be. But if you would prefer a more precise measurement, we've got something just for you.


What is 9 Inches in cm? And 4 inches?

As conversions go, turning inches into centimeters (cm) is not super difficult to do in your head. One inch is 2.54 centimeters. So four inches (the width of my hand) is just over 10 centimeters (10.16 cm to be exact). Six inches (the length of my hand) is still doable, 15.24, but it's getting to be quite a bit of math – and, we are not even looking at decimal measurements. If I were to do 9 inches, which is the length of my hand surfer-dude-style, I'd either need a pen and paper or this handy calculator.   

What about 9 cm in inches?

The inverse is a bit more complicated to do precisely. One centimeter (cm) is actually 0.3937008 inches. So, the best way to approach it is like this: You divide your measurement in centimeters by 10 and then multiply by four, and that's a good enough approximation. For higher precision, you can use this calculator.

The size of the inch (while bearing some relation to the width of the thumb of the average man in Scotland) had historically been defined as 'three grains of barley, dry and round, placed end to end, lengthwise,' before reaching the current standardized definition in the 20th century. 

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