# Millimeteres to inches - lenghth units conversion

1. mplanet62
Have a look at this http://www.metric-conversions.org/le...-to-inches.htm
Unbelievable! People were programming it, they store it on some server, and they need a computer fit enough for Moon landing calculations for such a simple task. What can be simpler? Just take size in mm, double it twice and shift decimal point two positions. I.e. 100 mm =100x2=200x2=400 - makes 4 inches. It's not precise, but blazingly quick and good enough to say that 100 mm aperture and 4 inch aperture is the same thing. In reverse: 5.2 in = 520/2=260/2=130 - roughly 130 mm. (132.08 mm precisely) Mistake is (132.08-103)/132.08x100 = 1.6%
Another good one - do you remember PI number? Yes, 3.14. The next 4 digits?
Here it is - 355/113. Mistake in 7th digit after the decimal point.
Have fun!
Michael
2. RichardJBartlett
Ha, didn't know that one (about the doubling)

I always used to divide by 25. Many kids use rulers in school that are 30cm/12in in length and from that I remember that there are 25mm (actually, 24.5, if I remember correctly) to the inch.
3. sxinias
Pi = 22/7 .... close enough for government work.
4. sxinias
Originally Posted by RichardJBartlett
Ha, didn't know that one (about the doubling)

I always used to divide by 25. Many kids use rulers in school that are 30cm/12in in length and from that I remember that there are 25mm (actually, 24.5, if I remember correctly) to the inch.

actually its 25.4 or there abouts.

Another easy way from inches to metric units is simply divide by 4 then multiply by 10 for cm or 100 for mm and the reverse for conversion from metric; not exact but very close.
5. JFD
Re: Millimeters to inches

Hello KISSers
Wouldn't a solar power calculator be more suitable??? Or a slide-rule??? Addition??? Multiplication???
150mm 150 x 2... 300 x 2... 6 inches! 150 x 4...??? 6 inches! 100 x 4... 4 inches! 80 x 2... 160 x 2... 3.2 inches 80 x 4... 3.2 inches!!!
KISSoff

This isn't Rocket Science...it's Astrophysics
JFD
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