One of the main issues with building to scale is that we are restricted by wheel sizes in game.
We have the choice of 3 block wide or 5 block wide wheels.
I only build in 3 wide wheels but this technique will work for 5 wide just as well.

So you need to choose are you going to use the small wheels (Off-road, racing, spiked, motorcycle)
Or are you going to use larger wheels (monster truck, drag, or truck)

Back to google
Search for a picture of your car
as an example I searched "ford focus 1993 side profile"
you want a picture that is side on as much as possible
The yellow car is a good example the Blue car is not.
What we want to do is change the size of the picture until the wheels are the correct scale in cm's
So in this case I want the wheels to be 3 cm's wide as I am going to be using 3 block wide wheels.
So grab a ruler and put it up on the screen and see if the car wheels are 3 cm's wide

Here you can see the wheel is 4 and a half cm's wide but we want it 3
sometimes if you are lucky you can change the zoom level on the web page hold cntrl and use the centre mouse wheel. or it will be in the browser menu somewhere.

but often the zoom will jump between to small or to large and you will need to download the image and resize it manually.

So this takes a bit of fiddling but I have made the spreadsheet to do this math for you.

Ok so what we want is to find a scale that allows you to use the wheel of your choice.

you need the measurements from Step 1 for the length and width of your car
and you will need to enter a number for how many blocks wide the car will be in game. I usually build to 8 Blocks wide.

the equation is =[Length]/([width]/car block width)
you might need to try a few block width variations until you find what fits
(this will be explained in the next step)

So I will use the ford focus as an example

4390 / (1823/8)
first we divide the width by the block width
4390 / 227.8
then we divide the rest and we are left with how many blocks long the car will be in game
19.27....
So 19 blocks long if we build to 8 blocks wide!

We are not done yet, because not all cars have the same size wheels in real life so this still might not match up with the scale we need.

you can skip this step if your where able to get the wheels to measure up to 3 or 5 cm's (depending on your chosen wheels)

save the picture to somewhere you are able to find it.


then open it up in paint or another picture editing program.
I right click on the icon and select edit and my computer automaticly opens it in Paint instead of photo viewer. Photo viewer has the same issue as the web browser the zoom is not adjustable enough.
otherwise select open with and find paint there


then you will need to resize the picture until the wheel measures the size you want
select


Select resize
make sure percentage is selected
then choose a number, smaller than 100 will make the number smaller the image.
a number larger then 100 will make the image larger.
if it was close you can press undo and try a little bit smaller or larger number.
experiment until the ruler matches up as we want


Now we just need to measure the complete length of the car


As we can see its about 20cm long
So now we go back to our Maths

So same maths as before, we age just checking that the 20 blocks long we measured was close enough. In our example I used 8 wide and that gave us 19 blocks as the correct scale length.
I'm happy with that being close enough.

otherwise if we changed the car block width to say 9 wide

the equation is =[Length]/([width]/car block width)

So I will use the ford focus as an example

4390 / (1823/9)
first we divide the width by the block width
4390 / 202.5
then we divide the rest and we are left with how many blocks long the car will be in game
21.6....
So 21 or 22 blocks long if we build to 9 blocks wide.

I suggest you stick to even width block sizes as you will find when using bumpers and other blocks that only come in even size's that it causes a lot of headaches.

Ok so now you can use your ruler to measure all kinds of parts on the image.


if you want you can collect pictures of the front, top and rear.
using the same technique you can resize them so that when you measure the width of the car it is around 8 cm's wide


That is it, you now have a way to measure and sort how many blocks wide and long you need your car to be, to keep it to scale, and can measure bonnet length and height, how long the roof is, how wide the grill is etc.

enjoy.

So the spreadsheet allows you to just enter the dimensions of your car and it will do all the maths for you, you just choose what scale works best with the wheels you are using.
The document has over 1000 cars and over 200 already have there measurements filled in.



https://1drv.ms/u/s!Agl_8VFOwTu0mX8oK0BvgqWJYBMJ?e=VdquqE
you will need to download this file if you want to add your own car/dimensions otherwise just use the cars already filled in.