Converting real life dimensions to HO

[scrag104]

Hello fellow railroaders,

I know that this is a stupid question but what is the equation to convert real world dimensions to HO? E.G. 40' real world equals how many inches in HO. I am drawing a real blank on the formula right now. Any help would be greatly appreciated.

Scott

[Tom Curtin]

The usual conversion factor is 87.1

[Throttle_JCKY]

One actual foot (12") equals 87 scale feet.

[pdt]

X x 12
______ = Y

87.1

where "X" is real world feet

and "Y" is inches

So, your example 40 x 12 = 480 inches
480 / 87.1 = 5.5109 inches

Clear as mud now?

[Sir Ray]

Not too exciting, but 1 inch (real) ~ 7.25 feet (HO)

This may help you estimate scale if you're in a discount store and see some potentionally useful toy vehicles or buildings which look like they are close to HO.

[NYC-BKO]

It is easier to use metric 3.5 mm equals one foot in HO.

Easier yet is to get a scale rule, which has HO scale feet, plus inches, I have a one foot one and a 6" one ( pocket size ) for taking with me to stores. Very useful tool.
There is a website where you can print one, but it eludes me right now, I can't remember which forum I saw it on.

Found the link to printable scale rule!
http://www.fiddlersgreen.net/images/n-horule.pdf

[scrag104]

Why and when did the scale change from 1/87 to 1/87.1? Thanks for giving me the conversion formula, I was drawing a real blank.

Thanks,
Scott

[scopelliti]

The ratio of 3.5 mm to the foot gives an exact ratio of

1 : 87.085714285714285714285714285714

Most folks round this to 1:87.1 or 1:87 which both have an error of less than .1 %

Modeling a one foot item at 1:87.1 vs exact scale would give a difference of two hundreth thousandths of an inch.

[Tom Curtin]

Wow --- love all those decimal places! You know, there may be some modelers out there who count those two hundred thousandths of an inch . . .

[retired grouch]

A reply to "scrag 104" and others

Many years ago, a member of the club to which I belonged at that time gave me the following formulae:

HO: Scale feet to actual inches where scale feet = X.
(1. (X) x .1379 = actual inches in thousands of inches

(2. take decimal number and multiply by .64 to get 64th of inch.

e.g. 20 scale feet
(1) 20 x .1379 = 2.758 (inches)
(2) .758 x .64 = 48512
(3) final solution =2-48/64" or round off to 2-3/4"


Since this is now also an N gauge forum also

(1. (X) x .075

e.g. 20 scale feet
-(1. 20 x .075 =1.5 (inches)


Try it. Pick a set of plans from your favorite model railroading mag. Get out the calculator, run the numbers, then double check with a ruler. But still go out and buy a scale ruler. Much easier.

Hope this helps.

Retired grouch in "Joisey"