Cartridge Loading Calculator
Moving-magnet cartridges are sensitive to capacitance. Your tonearm cable adds some, your phono stage adds some more, and the total affects how the treble behaves, so most makers publish a recommended range. This adds up what your system has and checks the total lands inside it.
The calculation assumes the standard 47 kΩ moving-magnet input, and it covers the electrical behaviour only. A cartridge's mechanical design is tuned on the assumption that it sees the recommended load, which is why staying inside the range matters more than chasing any single figure. Moving-coil cartridges barely react to capacitance, so this calculator is for moving-magnet and moving-iron types. If you don't know your phono stage's input capacitance, its manual usually lists it.