Circumference is the distance around the outside of a circle – or in our case, a tube. It is calculated by multiplying pi times the diameter.
In rocketry, there are so many different sized tubes out there. Just because a tube is advertised as a 2″ tube doesn’t mean it’s actually 2″. Some manufacturers’ 2″ tubes are actually 1.9″ (like Aerotech). Estes made a BT67 that was 2.02″ and a BT70 that was 2.217″. For a long time, standard 5.5″ tube was actually 5.38″, for example. For this reason, there are far too many circumference sizes to list each one, so we ask you to provide a circumference.
PLEASE ALSO REMEMBER WHAT A TUBE IS ADVERTISED TO BE IS ALMOST NEVER CORRECT! it may say its a 4″ tube but chances are its either 3.91 or 4.12″ (these are BOTH very common)
When finding your circumference, DO NOT simply “do the math” or use calipers to take your measurement then do the math. More often than not, you’ll squeeze the tube (even just a tiny bit) when measuring diameter/radius, which will give you the wrong number right from the get-go and your math will be wrong, ACTUALLY IT WILL MULTIPLY YOUR SMALL ERROR BY 3.1415 NOW making it a HUGE error. (if you squeeze your tube just 1/8″ you will be off by almost 1/2″ when doing the math!!!!) . Instead, please physically wrap something (such as a piece of paper, tape or measuring tape) around your tube, mark it, and measure it to get an exact circumference. (THIS METHOD WILL ALWAYS BE CORRECT EVEN IF YOU SMASH THE TUBE BY 2 INCHES!) Then, when you make your order, select the closest Diameter size listed and then enter your exact circumference measurement! That way, we can adjust the decal size to fit your tube exactly!
IF your tube is a standard tube with no extra fiberglass or super thick paint etc. you can enter ” MADCOW THINWALL FIBERGLASS” or “PML PHENOLIC TUBE” etc I do have measurements for MOST standard HIGH POWER tubes. BUT entering your TRUE Circumference will ALWAYS give you the BEST matched decal for your rocket.