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Random numbers

There is a random number generator in Roblox that seems to generate random numbers. But do a test, and insert this script into your place:

for _ = 1, 10 do

Test the place, and look at the output window. Write down the numbers you get, and exit the test. Then do the test again, and again write down the numbers you get. Notice something weird? Those 10 very random numbers are similar everytime you run a test (or play online for that matter).

This article explains how to achieve truly random numbers that are not the same every time a place is played.

The General Idea

Every time a script in a place uses the math.random function, the random generator generates a random number. However, the random number generator is deterministic. It uses the last random number to generate the next random number. When the scripts starts, the "first" random number is always the same. So every time the script is ran, the same random number sequence will be generated, as in the test at the top of this page.

Generating Different Random Numbers Every Time the Game Runs

To receive a different value every time the function is called, you need to set the seed to a different value when the game runs or to call the math.random function a random number of times, if you want to get different numbers every time. Some truly random events can be things like:

  • Players' movement speed
  • Other real-life influences on the game
  • The chances of getting an item or map with the usage of a table

There are 2 ways you can make the random number generator generate different numbers every time the place runs:

  • call math.random a random (from real-life influences) number of times
  • Seed the random generator with a different number whenever the game runs

If you can find a way to make something truly random influence any of the two listed items, then you will be able to generate different numbers every time the game runs.


The best way to fix this problem is setting the seed of math.random() with the function called math.randomseed().

The problem is finding a good seed. One option is to use tick(). This returns the number of seconds elapsed since UNIX time (1/1/1970 0:00:00).

To use it, simply pass the result of tick() to math.randomseed.


Using the Seed

You could use math.randomseed anywhere. It is recommended to put it at the beginning of the script (it doesn't really matter, as long as you put it before you use math.random). Now, let's use the experiment script that we used before and use math.randomseed with it!

for _ = 1, 10 do

Congratulations! Your random numbers will now be different every time the place runs!

Even more random

When doing something like math.random(1, 100), all the numbers will turn out as whole numbers, which in some cases, just isn't enough. However, if you did this, then the numbers would be random non-integers between 1 and 100, including decimals:

for _ = 1, 10 do

This proves that when calling the math.random() function with no arguments provided will give you a number between 0 and 1.


Exercise 1


Make a function that returns a string representation of a random card from a standard deck of cards.

function getRandomCard() 
  local number = math.random(13)
  local suit = math.random(4)
  local card = ""
  if number >= 1 and number <= 9 then card = number + 1
  elseif number == 10 then card = "Jack"
  elseif number == 11 then card = "Queen"
  elseif number == 12 then card = "King"
  elseif number == 13 then card = "Ace"
  else card = "?" end
  card = card .. " of "
  if suit == 1 then card = card .. "Hearts"
  elseif suit == 2 then card = card .. "Diamonds"
  elseif suit == 3 then card = card .. "Clubs"
  elseif suit == 4 then card = card .. "Spades"
  else card = card .. "?" end
  return card

Exercise 2


'Reword this!' Make a function that returns true a certain percentage of the time and returns false a certain percentage of the time. Allow the percentage to be specified as a parameter to the function.

function getResult(percentage)
  return math.random() <= percentage

See also