How do scales work?

Can someone tell me how to calculate scales out because they really confuse me. Thanks

if its given in meters multiply by 1000 to get mm and then divide by the scale, then just figure out if you can do it easily in your head. on a scale of 1:500, 20meters x 1000 = 20000, divide it by 500 and you get 40mm. so you can just double the figure given

jst change them to mm and devide by the number on the right side of the ratio eg. 40cm and its 1:20, change it to 400mm then devide by 20 = 20mm. You can do this for all of them.

tygrys1—