Random Number Generator

Pick one or many random numbers in any range — with an option for no repeats. Everything runs in your browser; nothing is sent anywhere.

Written by the Calculator Index team · Last reviewed September 2026

Check your inputs — max must exceed min, and unique count can't exceed the range size.

Random result
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How it works

Each number is drawn uniformly from the inclusive range you set, so every value between the minimum and maximum is equally likely. With "no repeats" enabled, drawn numbers are removed from the pool, which is what you want for raffles, random team assignments, or picking lottery-style numbers. The generator uses your device's built-in randomness — fast, private, and free.

value = min + floor(random × (max − min + 1))

Good uses (and one caution)

This is perfect for deciding who goes first, drawing a raffle winner, sampling rows from a list, rolling custom dice, or breaking a tie. One important limit: browser pseudo-randomness is not cryptographically secure — don't use it to generate passwords, security tokens, or anything real-money. For those, use a dedicated secure generator. For picking from named options rather than numbers, assign each option a number and draw one.

Worked example — running a 3-winner raffle from 250 entries

You sold 250 raffle tickets, numbered 1 through 250, and need to draw 3 distinct winners. Set minimum = 1, maximum = 250, count = 3, and enable "no repeats."

The generator removes each drawn number from the pool of 250 before the next draw, so a result like 187, 42, 219 is guaranteed to contain three different ticket numbers — no risk of drawing the same entrant twice, which "allow repeats" would not guarantee.

Worked example — why repeats sneak up on you in a small range

Rolling a standard 6-sided die (range 1–6) five times in a row, with repeats allowed, feels like it should rarely produce a repeat — but the chance of no repeat at all is only 6/6 × 5/6 × 4/6 × 3/6 × 2/6 ≈ 9.3%. That means there's roughly a 91% chance at least one number repeats across five rolls, which is exactly why "no repeats" exists as an option for tasks where duplicates would be a problem.

What "pseudo-random" actually means

Nothing generated by a computer is truly random in the philosophical sense — it's produced by a deterministic algorithm seeded with an unpredictable input, like the current time. For everyday purposes (games, raffles, sampling) this is functionally indistinguishable from true randomness. The distinction only matters for cryptography and security, where an attacker who could predict the seed could predict the output — which is exactly why this tool, like most browser-based generators, isn't suitable for anything security-related.

Common random number generator mistakes

Frequently asked questions

How does a random number generator work?

It uses your browser's pseudo-random generator to pick uniformly within the range, on your device.

Can I generate numbers with no repeats?

Yes — enable "no repeats" for unique draws; count can't exceed the range size.

Is this suitable for security or gambling?

No — it's not cryptographically secure. Fine for games and draws only.

What does "pseudo-random" mean?

It means the numbers come from a deterministic algorithm seeded with an unpredictable value, which is indistinguishable from true randomness for everyday use but not secure enough for cryptography, where a predictable seed could be exploited.

How do I run a fair raffle with this tool?

Number entries 1 to N, set the range to 1-N, enable "no repeats," and draw as many winners as needed — each draw removes that number from the pool.

Why does "no repeats" matter for a small range?

Repeats happen more often than expected in a small range — five rolls of a 6-sided die have roughly a 91% chance of at least one repeat with repeats allowed.

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Last reviewed: September 2026.