The maximum load that an adult donkey can carry on its back is 20% of its body weight. A formula is recommended by the Swiss Confederation for calculating the maximum load: height at the withers (cm) x 0.83 – 50.
A small-sized donkey (up to a height at the withers of 105 cm) can therefore carry up to 37 kg, a normal-sized donkey (up to a height at the withers of 106-135 cm) up to 62 kg, and a large-sized donkey (up to a height at the withers of 136-155 cm) up to 79 kg.