 # Math to scale down real life dimensions into any imperial scale

I want to scale down a coffee table. What I been doing so far is divided the number with the scale I’m going to use.

For example I’m using the 1/8”=1’-0” scale,

118cm (46 1/2”) x 78cm (30 3/4”).

118/8 = 14.75
78/8 = 9.75

So I take that and turn it into 14’ 7” x 9’ 7”.

I’m wondering if I’m doing that right or my dimensions are wrong.

I’m wondering why you are doing all that math. There are several ways I can think of to scale the model down. Easiest would be to use the Tape Measure tool to measure an edge that is 12 inches long, type 1/8 or .125 and hit Enter. SketchUp will ask if you want to resize the model. What are you going to do with the scaled down model?

Ohh I didn’t know there was a easier way to scale down and it’s for a school project I’m doing.

Well, maybe you’re supposed to be doing the math then?

No I am not sure about your math but I don’t think it is right… I rarely deal with the metric- imperial divide, except with products.

So I think you mean you are starting with a model and you know the metric
sizes. (or even a real object) at full scale, and you want to know how big it is in (or scale it down to ) 1/8" = 1’-0" scale.

SketchUp can do it for you of course as Dave says OR in SU you can also scale the model by the correct ratio, and then just change the units.

To do so you should know the ratio that relates to the scale. In this case it is 1:96. So you just scale the model down 1/96. Oddly SU won’t take this number. but you can use the decimal .01.

If you have a real object at 118 cm. it would measure. 1.18 cm in a 1/8"=1’-0" scale drawing, (which is roughly .5 inches).

To get the ratio you divide by 12 so 1/8 / 12=.01 or 1:96. Also e.g. 3"=1’-0" is .25 or 1:4 scale ratio.

The equation 118/8=14.75 = 14’-7" is suspect. I’d leave that process out altogether. Maybe this is the new math and it’s too late at night here, but I’d do it differently.

You seem to be wanting to make both a scale drawing and units conversion. However, you don’t want to mix the two. Deal with these separately. I wonder what the assignment or purpose is.

Your conversion to the table’s dimension look close. but for scaling the drawing, all that’s needed is the ratio, and that tells you what the drawing will scale down to.

Also I think you are using the decimal incorrectly. The decimal number in the imperial system does not relate to “feet and inches”, It can only relate to one or the other . For an example civil engineering plans often use decimal feet. However 10.5’ is NOT 10’-5", it is 10’-6", because there are 12 inches in a foot.

If you are a metric user, you can now get an idea what we suffer with in the U.S. But we have to keep on top of this for the near future or we may mess up our space missions terribly.

In SketchUp we usually draw at 1:1 and only make it a scale drawing in the printing or LayOut process.

In a final gasp of pedantry: If you are doing furniture drawings. 1/8"=1’-0" is probably too small a scale to be useful.

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Experiment with Window menu → Model infos → Units.

Select a metric unit (m, cm or mm) or an imperial unit (in, ft or yard) depending of the values that you have. According to your post, it looks like you need to select unit in the metric system.

Then, when your model is done, you can select again the previous menu and select units in the other system which will probably be the imperial system. Then, whenever you use the Measuring tool or the Dimension tool, you will get the units automatically converted in the other system.

If you really want to scale down, you can use Dave’s suggestion.

Maybe Eneroth Object Scale is what you need? It let’s you size objects by entering sales such as “1:100” or “1m = 4y”. (I’m using it myself for the model railway!)

https://extensions.sketchup.com/extension/992485bd-ebf9-4d0d-a874-4cd097b21133/eneroth-object-scale

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Why are you mixing imperial scales and metric units, which is leading to confusion. 1/8" = 1’0" or 1:96 is indeed a common imperial scale ratio, as are 1:24 1:48 and 1:12. These are all scale ratios that are appropriate for a fractional 12 based system.

The metric system is 10 based. Common metric scales are 1:100, 1:50, 1:20, 1:10 and 1:5.

Applying a 1:96 scale to a metric measurement is possible I guess, but a headache. If 118 cm is the real world measurement, then the scaled drawing dimension would be 1/96th of that. 118 ÷ 96 = 1.229166666666667, This is why imperial scales are 12 based and metric scales 10, so that whole units tend to scale into other whole units.

If you are working with metric then 1:100 is a much easier scale to use.

It’s for a school project, maybe that’s why. But there’s confusion when speaking of drawing scale and conversion of units at once.