There are a few different tools you can use to cut off a lock. Bolt cutters are the most common. Simply clip off the lock's shackle to remove it. You could also use an angle grinder and cut through the shackle, but you'll need to secure it with vice grips and wear face protection to protect against flying sparks.

What's the best tool for cutting off a padlock?

Bolt cutters are the common tool of choice for to cut padlocks during forcible-entry. Unfortunately, most padlocks are made of case-hardened steel, which is very strong in comparison to the materials that bolt cutters were intended to cut.

What tool do you need to cut a lock?

The simplest tool for cutting locks is the bolt cutter. Essentially it is just a reinforced pair of scissors with a fulcrum joint for additional power. Bolt cutters come in a variety of sizes, with the longer-handled ones giving you more leverage for greater power.