Work out random number entropy instantly with clear inputs, formula shown and shareable results.
A byte only carries eight bits of entropy if the source is ideal; real sources produce less, so producing full-entropy output requires collecting proportionally more raw bytes and conditioning them through a hash or extractor. The source class matters more than the quantity: a non-cryptographic generator such as Math.random is predictable from a handful of outputs no matter how many bytes you draw.
Entropy accounting
total entropy = output bytes x entropy per byte; raw bytes needed = ceil(output bits / entropy per byte)
The operating system CSPRNG — getrandom or /dev/urandom on Linux, BCryptGenRandom on Windows, SecRandomCopyBytes on Apple platforms — or your language's crypto-specific random function.
Modern kernels seed a CSPRNG once and then generate indefinitely, so blocking on entropy is only a concern at very early boot on devices without a hardware RNG.