Need a site that calculates ratio

[Phait]

Not aspect ratio. Working on a drawing, the length of a rifle I printed is 6.5 inches, the guy in the drawing is 9.5 about.

So, trying to gather the real length of a Dragunov (48 inches) with someone who is 72 inches tall, I need to compare ratios to make sure I have the drawing scale right

6.5" : 9.5"

48 : 72

that kinda thing, I need to see if they are the same proportion just at different scales.

Like in this image, the RED is small scale (6 and 9 squares tall), BLUE is large scale (48 and 72 squares tall). By copying the large and sizing it down keeping proportions, I can see the ratio is not the same, as the smaller blue line is not the same height as the small red line. I just need to know what the ratio difference is.

http://img12.imageshack.us/img12/2633/43090018.jpg

[Bludd]

Tried the Google calculator (http://www.google.com/search?q=6.5+inches+%2F+9.5+inches)?

[Phait]

Oh so you divide the smaller value by the larger?

[Bludd]

Well, not really. The values are interchangeable provided you compare the result to another result gained from a calculation where the variables were in the same place.

So it's length/width or width/length but you have to stick to one of them if your comparisons are to be valid.

Edit: Playing with the numbers, I found this

(6.4 inches / 9.6 inches) = (48 inches / 72 inches) or said differently (6.4 inches / 9.6 inches) / (48 inches / 72 inches) = 1

[Mr.Fibbles]

I like to just use Excel to do my complicated calculations like this. Using Spreadsheet is an easy way to do things like this. Of course, you need to know the formulae.

[Bludd]

This is complicated? :cool:

[Daedolon]

I'm not sure but don't you just want to get the % of the difference and add/subtract it to the other value as well?

Might be thinking about completely different thing though.

[Bludd]

No, you have to multiply or divide.

4:3 is the same ratio as 8:6 as is 12:9 and 16:12

So if you want to know x:9 you multiply 9 with (4/3)
Or if you want to know 16:y you divide 16 by (4/3)

[Daedolon]

No, you have to multiply or divide.

That's what I meant, yeah.

[Phait]

Well Bludd is right, I divided and got answers like 0.68 and 0.66 - so my 2 proportions were close but not exact. So, I may have the right scale for my drawing. Still when I eyeball it, I feel a bit unsure.

[Bludd]

Use 6.4 inches and 9.6 inches instead of 6.5 and 9.5.

[peoplessi]

http://static.iltalehti.fi/uutiset/suomalaisaseSTL_uu.jpg

SAKO TRG-42 on his back, length is 1200 mm = 47,2" - so tad shorter than Dragunov, but you get the idea that it will look a lot disproportioned.

[KO Gilligan]

You should have one of these handy gadgets and you won't need to calculate.
It's a printer/graphic art tool called a proportion wheel

Find it in most art stores for like $7

once you turn it to match one set of measurements, it's a quick guide to convert any number by the same ratio

http://i44.tinypic.com/4kpy8.jpg

So I googled Online Proportion Wheel
An online version is here:

http://www.copyitmailit.com/p.htm

---------- Post added at 07:19 AM ---------- Previous post was at 07:06 AM ----------

Oh so you divide the smaller value by the larger?

yes or vise versa

then that is your ratio by percent:D

[Nessus]

Just do this.

6.5 divided by 9.5 = .6842 So now multiply 72 by .6842 and you get 49.26

[Bludd]

When did this turn into mathematics for children? If you've gone to school, you should know this!