Hi all My math isn't what it used to be so I am floundering with a drawing I have. The drawing is of an engine house and I have a number of fixed dimensions but there is no scale defined. I am looking for help working it out so I can plot all the dimensions to start building the thing from scratch. For example I have one dimension, 66' which equals an actual 128mm (close to 5 1/16) on the drawing, another is 13' which is an actual 24mm (15/16). I am trying draw a full size plan for HO scale. But working out the scale of the drawing has me stumped. Can anyone help a math dunce with this one? Cheers Bruce

Go to your LHS and purchase a scale ruler. If the diagram measures 60' then draw the 60' on the HO ruler and it will all follow suit.

Thanks for that but.... I have a scale rule. The problem is that there are unmarked dimensions and so I need to find the scale of the drawing to find the correct dimensions for those. Cheers Bruce

The way I do it is probably more complicated but here goes. Take the full-sized dimension and multiply it by 12 to get the number of inches. Since HO is 1/87th scale I divide the number of inches by 87 which gives me the number of scale inches. In this case it would be 66 X 12 = 792. Then 792 divided by 87 = 9.1034 inches. A tip to figure out the fraction is to subtract everything to the left of the decimal (9) and multiply what's left (.1034, [include the decimal point]) by 16 which would be 1.65. This is the number of 16ths of an inch to add to the 9 inches, so 66 feet would work out to 9 and 1 1/2 16ths (or 3/32) inches. Not super accurate for rivit counters but it gets you in the ball park. :sleeping: :sleeping: (Feet X 12) divided by 87 = xx.yyy scale inches; xx.yyy - xx = .yyy 16ths; .yyy X 16 = zz 16ths of an inch. Feet actual would be xx and zz 16ths HO scale inches. Clear as mud???

Wow Pitchwife, that's some math there....Thanks for the effort. But (again), my problem is more of unscaled, unmarked dimensions. For example, the length is 128mm (66'), width is (by the looks) 64.5mm (33') and the height is 37mm (???? feet). It is the scale to get the ??? feet that I am working on. Once I have a scale, then it is simple from there (sort of). Now in inches (as indciated earlier), I think it is 5/64" = 1' but I could be wrong. Cheers Bruce

OK, I think I see what you are doing. You need to determine what scale the drawing is to get the remaining dimensions, right? First I'd lose the metric measurements. Everyone else in the world might disagree but thats their tough luck. On the drawing 66' = 5 1/16 or 5.0625 inches. 66 X 12 = 792 inches. 5.0625 divided by 792 = .006392 or 1/156.444. So your scale is 1/156.444. N is 1/160 so if you used the N scale of your ruler and then convert that to the HO scale you should come close. Hope this helped.

Wow nice math skills!! Well I couldnt help on any of the math but I sure would like to see a picture of these drawings when your done. Sounds like a fun project though!!! Eric

Bruce, do I get you right and you measure in millimeters? If so, the math gets somewhat easier! Now let's see: You measured... 128 mm on the drawing, representing a real length of 66 ft (20.13 meters) --> in H0 (scale 1/87) this should be 231.4 mm (length) 64.5 mm on the drawing, representing a real length of 33 ft (10.065 meters) --> in H0 this should be 115.7 mm (width) Since the prototype size (66ft & 33 ft) are 2:1, the measurements on the plan should also be 2:1. But it is 128:64.5 so there is a very slight distortion of about 1% (which really doesn't matter at all ) Now you ask: How high is the shed, when you measure 37 mm? Ok, we know that 128 mm on your plan will be 231 mm in your H0 model. 231 divided by 128 equals 1.805 - I'd say for a model of that size 1.8 is exact enough. So all you have to do is to take ANY measurement on your plan in millimeters and multiply it by 1.8 ---> there is your H0 dimension! :thumb: --> So your shed will be 67 mm high (66.6mm, to be more exact). Happy drawing and modeling! Ron PS: Clark, you see - sometimes metric measurements has its advantages, too! But your trick with the scale ruler hits the nail on the head!

Excellent stuff! This is great. Thanks Ron, it is now in my more "native" measurement - yup, Australia is metric. I will now get measuring and converting to HO feet/inches while I am at it. Thanks all for your great help. Cheers Bruce

A quick shortcut that sometimes works is to scan the image and enlarge/reduce it until the print matches your scale ruler for a given known. Works great for smaller scales and structures until the buildings get bigger than the paper. FRED

Ron, us poor Americans have just never figured out what to do with those extra 3.37 inches that are left over from each yard.