http://www.industrial-enclosures.com/html/conversion-mm-inch.html
Assuming the question is in regard to firearms and ammunition, you can read the "caliber" of a round as a decimal how wide the bullet is in inches. So a .40 caliber round is .4 inches wide, or about 10.16 millimeters wide. A .45 caliber round would be .45", so a little bit fatter than the .40 caliber round. The caliber doesn't tell the whole story of a round though, it doesn't say how long the bullet is, how heavy, how big the casing behind the round is, how much kinetic energy is hits with, etc. The .40 S&W round has an average of 425 ft/lbs of energy right at the muzzle, while the .45 ACP, a "bigger" round, has about 400 ft/lbs.
They're both measurements of the diameter of the round (or the barrel). Caliber is a measurement in inches, and millimeters are millimeters. For instance, a .30 caliber bullet is 30 hundredths of an inch, or 7.62 millimeters in diameter.
Size and relative power. A .40 caliber bullet is .40 of an inch and the entire cartridge is 28.8 millimeters long. A .50 caliber (handgun) bullet is .50 of an inch and the entire cartridge is 40.99 millimeters long. The .50 caliber has more powder, more velocity, and more muzzle energy.
.4005 inches.
In excess of a mile.
The AK-47 assault rifle is chambered for the 7.62x39mm round, which is of the 7.62 millimeter caliber.
No. 9mm and .40 are not interchangeable.
A .45 caliber bullet typically measures 11.43 millimeters in diameter.
.40 Smith & Wesson is a 10x22mm cartridge, whereas the .45 ACP would measure 11.65x23 in metric measurements. The .45 is a larger round, and also a much slower round.
Caliber means the diameter of the bullet. A .40 caliber cartridge has a bullet that is .40 inches in diameter. A 9mm cartridge has a bullet that is 9 millimeters in diameter. Yup...reminds me of Joe the Human Cannonball at the circus...Poor Joe died but they couldn't find a replacement of his caliber.
It depends on several factors, but a good rule of thumb is "about a mile."
my opinion is the 45 ACP round has more knock down powder then the 40 caliber