I believe the calculation steps are quite complex to give a simple formula or even to follow it by hand.
Maybe this medium article and the cited paper gives you a better general understanding.
As you can see in the article and paper, QV takes into account various factors other than error rates e.g. calibration and circuit optimization.
IBM successfully ran this exact test to achieve a Quantum Volume of 64 on its 27 qubit “Montreal” system — and the test didn’t even require building a new device. Instead, the team incorporated improvements to the Qiskit compiler, refined the calibration of the two-qubit gates, and issued upgrades to the noise handling and readout based on tweaks to the microwave pulses and gates before they’re applied in the circuit.
metric takes into account all relevant hardware parameters. This includes the performance parameters (coherence, calibration errors, crosstalk, spectator errors, gate
fidelity, measurement fidelity, initialization fidelity) as
well as the design parameters such as connectivity and
gate set. It also includes the software behind the circuit optimization.
The simplest explanation from medium article would be:
2 to the power of the depth of the largest square circuit (width=depth), which you were able to run on your device successfully with greater than two-thirds probability and confidence interval greater than 97.725%, gives you QV.