How to Generate Random Numbers Without Repeats

What “without repeats” means

A draw without repeats removes each selected number from the pool. If you draw 7 from 1 through 20, the next draw can use any allowed number except 7. This is also called sampling without replacement.

A draw with repeats leaves the number in the pool. The same number can appear again. Neither setting is always better; the right one depends on the task.

When unique numbers help

Use unique numbers for raffle tickets, bingo calls, seat numbers, and samples where one row should be chosen at most once. Open the Unique Random Number Generator, set the range and quantity, and add any values that must be excluded.

Check the size of the pool

You cannot request more unique results than the pool contains. The range 1 through 10 has ten numbers. If you exclude 3 and 8, only eight numbers remain. A clear generator should stop and explain the problem instead of returning duplicates.

Order can matter

A set of unique numbers tells you which values were picked. A random sequence also tells you their order. Use the Random Sequence Generator when first, second, and later positions matter.

Do not confuse unique with secret

A number can be unique in one draw without being hard to guess. Ticket numbers and sample row numbers are often public. For secret codes or passwords, use a tool made for security and keep the result private.

A simple example

A teacher wants five different question numbers from a list of 30. The teacher sets 1 as the minimum, 30 as the maximum, and 5 as the quantity. With repeats turned off, every returned question number is different.

For choosing full rows instead of their numbers, read the sampling checklist and use the Random Sample Generator.