Need Help With Decal Sizing

Hi everyone ! I know this is a weird question but I need help on the sizing of the OEM Stickers for certain Machines that I have so that I can put my company logo on the machines. If you have any suggestions where to place a company logo and how big that would be great too! Models John Deere - 200 Excavator Komatsu - PC200LC-8 Caterpillar 320 (2005) Caterpillar 320 L D5G Bulldozer 938 Loader Caterpillar 304 Caterpillar Roller Kubota Tractor Thanks Guys!