Minecraft wiki entry for Firework_Rocket, associated text: The height it rises is between 8 and 20 blocks with 1 gunpowder, 18 to 34 blocks with 2 gunpowder, and 32 to 52 blocks with 3 gunpowder. (Note: Using command blocks, firework rockets with higher durations go higher and keep accelerating with virtually no terminal velocity. If the duration is long enough, the firework rocket could reach heights of over 1000000 blocks and speeds of over 10000 m/s in a matter of minutes. Such fireworks with significant X and Z motions speed up sideways exponentially and reach outside the world boundary in a matter of seconds.‌[Java Edition only])