  Fault-tolerant schemes can use error correction to make a quantum computation
arbitrarily ac- curate, provided that errors per physical component are smaller
than a certain threshold and in- dependent of the computer size. However in
current experiments, physical resource limitations like energy, volume or
available bandwidth induce error rates that typically grow as the computer
grows. Taking into account these constraints, we show that the amount of error
correction can be opti- mized, leading to a maximum attainable computational
accuracy. We find this maximum for generic situations where noise is
scale-dependent. By inverting the logic, we provide experimenters with a tool
to finding the minimum resources required to run an algorithm with a given
computational accuracy. When combined with a full-stack quantum computing
model, this provides the basis for energetic estimates of future large-scale
quantum computers.
