Loose top soil weighs about 1.5 tonnes per cubic metre.
A standard wheelie bin has dimensions approx 50cm x 55cm x 100cm, or 0.27 cubic metres. A wheelie bin therefore can take 400Kg of top soil.
Hence 2.5 wheelie bins.
PS You'd be ill-advised to try this - wheelie bins are not designed to accommodate dense materials. At best the wheels will probably collapse, or worse the sides may split open.