If everything seems under control, you're not going fast enough. ~Mario Andretti 🏁

Die-Cast Model Sizing

Scale Size

1:64 Size is a model approximately 2.5 to 3 inches in length (most common size) 

1:43 Size is a model approximately 3 to 5 inches in length

1:24 Size is a model approximately 5 to 8 inches in length

1:18 Size is a model approximately 8 to 11 inches in length

1:12 Size is a model approximately 14 to 16 inches in length

Here is a Wiki detailed list