DC Cable Size and Voltage Drop

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Cable size and voltage drop (DC, 12 V / 24 V / 48 V)
Too thin a cable wastes power and heats up. Check before you buy.
Inputs
systemVoltage = 12 V
loadPower = 300 W Length one way, the current flows there and back
cableLength = 5 m
crossSection = 6 mm^2 Annealed copper at 20 C: 1/58 ohm mm^2/m (IEC 60028 standard value), warm cables have about 20 % more
copperResistivity = 0.0172 ohm mm^2 / m
maxDrop = 3 % Current and resistance
current = loadPower / systemVoltage to A
resistance = copperResistivity * 2 * cableLength / crossSection to ohm Voltage drop
drop = current * resistance to V
dropShare = drop / systemVoltage
lostPower = current^2 * resistance to W Is this cable big enough? Smallest cross section for the allowed drop
neededCrossSection = copperResistivity * 2 * cableLength * current / (maxDrop * systemVoltage) to mm^2