[Steve Mavronis]

What scale is 3/4 inch per foot? Some say it's 1/18th scale and I say it should be called 1/16th scale, since there is a 1:16 ratio between 0.75" and 12".

In my mind if I'm using a scale of 3/4" per foot, and I have a 1 foot long real world object the model of it would be 3/4" long. 16 of these 3/4" models end to end would measure a total of 1 foot long.

 

[Trek Ace]

You are correct.

3/4" = 1' is 1/16th scale.

1/18th scale is 2/3" = 1'.

 

[Steve Mavronis]

Thanks Trek Ace, my sanity is back. Now off to convince this certain someone, who I'm hoping is just confusing 18 with 16...

 

[StarshipClass]

I'm glad I'm not the only one who gets confused over that kind of thing sometimes. Usually I have to leave it to later when my brain starts working again

 

[jackshield]

What scale is 3/4 inch per foot? Some say it's 1/18th scale and I say it should be called 1/16th scale, since there is a 1:16 ratio between 0.75" and 12".

In my mind if I'm using a scale of 3/4" per foot, and I have a 1 foot long real world object the model of it would be 3/4" long. 16 of these 3/4" models end to end would measure a total of 1 foot long.

Yet someone told me for 1/18th scale if you have a 6 foot object you are modeling you would multiply 3/4 times 6 and get 4.5 inches. Ok, but in reverse if I take 6 feet and convert to 72 inches and divide by 18 (which should be 1/18th the original size) you get 4 inches and not 4.5 inches! This is a paradox for me.

When scaling down something measured in feet to inches, aren't you supposed to keep the units the same during the math calculation, for example you should convert feet to inches to scale inches to inches and not feet directly to inches, right?

COMING FROM THE PROFESSIONAL DRAFTING ARENA...
WHEN ALL ELSE FAILS, DO THEY MATH...
SCALES ARE RATIOS
12/.75=16

 

[Steve Mavronis]

Yes using Ratios is the easiest way of understanding it. A lot of times I use the mathematical laws of proportions where you cross multiply to figure scaling out by solving for the missing value you want to know. Just make sure you have the order of comparison correct:

A/a = B/?

gets you:

? = aB/A

You would say it like; A is to a as B is to ?

Or you could do A is to B as a is to ? like this:

A/B = a/? and you cross multiply and get ? = aB/A

You see it's the same.

 

[John P]

Well, since a scale IS a ratio, yeah....

 

[StarshipClass]

Yet someone told me for 1/18th scale if you have a 6 foot object you are modeling you would multiply 3/4 times 6 and get 4.5 inches. Ok, but in reverse if I take 6 feet and convert to 72 inches and divide by 18 (which should be 1/18th the original size) you get 4 inches and not 4.5 inches! This is a paradox for me.

When scaling down something measured in feet to inches, aren't you supposed to keep the units the same during the math calculation, for example you should convert feet to inches to scale inches to inches and not feet directly to inches, right?

Yeah, I can see it now.

3/4" per foot is 1/16th since 12"/.75"=16. Your friend's not converting feet to inches resulted in an error of 2" for every 12" which made it appear to be 1/18th instead of 1/16th.

 

[Steve Mavronis]

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