How Many Different Keys Does One Set Of Padlocks Have?

Padlocks are produced with a set number of unique key combinations, known as differs. After a certain number of locks are manufactured, these key combinations eventually repeat. This is unavoidable because padlocks use a pin tumbler mechanism with a limited number of possible pin height combinations.

Why Differs Matter

For most single padlocks, the chance of someone else having the same key is extremely low, especially across different brands that use different key blanks. However, differs become important when large numbers of identical padlocks are used in the same place.
For example, schools often install hundreds of the same padlock on lockers. Without enough differs, students may discover that their key opens someone else’s locker, and this can spread quickly.

High vs Low Differ Counts

Two main factors affect the number of differs in a padlock:

• Padlock size (number of pins)

• Build quality and manufacturer tolerance

Smaller and cheaper padlocks have fewer internal pins and less precise components, which reduces the number of possible key combinations. This can lead to key repeats in large batches.

Examples Of Low Differ Risks

In some small or low-cost padlocks, true differs can be as low as 15.
In a batch of 100 padlocks:

• Each differ would repeat around 6 times
  This means multiple keys would open multiple lockers.

How Pin Combinations Create Differs

Each pin in a lock can be cut to a number of heights. If a padlock has:

• 3 pins, each with 5 possible heights → 5³ = 125 theoretical differs

• 5 pins, each with 5 heights → 5⁵ = 3,125 theoretical differs

However, the true differ is often lower due to manufacturing tolerances. Two keys that are technically different may still operate the same lock if the cuts are close in size.

True Differ Testing

Manufacturers publish technical differ numbers, but these can be misleading. The more accurate measurement is the true differ, which is determined by physically testing a large batch.
In practice, ABUS is one of the few brands with consistent true differ performance across sizes.

Typical ABUS True Differ Counts

• 15mm padlock: 16 differs (3 pins)

• 20mm padlock: 40 differs (3 pins)

• 30mm padlock: 200 differs (4 pins)

• 40mm padlock: 540 differs (5 pins)

• 50mm padlock: 1000+ differs (5 pins)

Practical Recommendation

For locker systems, stockrooms, gyms, schools and shared-use areas:

• Choose 30mm padlocks or larger
  Below 30mm, repeat key combinations become more likely.