Qubits vs noise

Physical error rate per operation: 0.50% Code distance d (bigger = more physical qubits per logical qubit): 7

Stylised rule of thumb: logical error ≈ 0.1 × (p / p_th)^(d+1)/2, with threshold p_th = 1% and about 2d² physical qubits per logical qubit (surface-code style). Real thresholds, constants and overheads differ by hardware and code. Below threshold, a bigger code helps; above it, a bigger code hurts.