Roblox only sells Robux in fixed package sizes, not at a flat per-Robux rate, so the cheapest way to reach a target amount is usually some combination of packages rather than just one. This works out that combination using the commonly listed package prices, and Roblox Premium's purchase bonus if you have it.
Roblox Premium currently adds a commonly cited 10% bonus Robux on purchases - leave this at 0 if you don't have Premium.
Total Cost
$0.00
Robux You'll Receive
0 R$
Enter how much Robux you want.