With an empty inventory:
Body strength required = Total weight / 70 (Didn't think it was that easy now huh?)
Body strength required = (Cargo weight + Cart weight) / 10 / 7 (See the resemblenceresemblance?)
For example, someone with 21 body strength carrying 20kg of tools could drag a small cart, which weights 60kg, filled with up to (21BS * 7 - 20kg) * 10 - 60kg = 1210kg, which is 80 [[stone brick]]s. Remember the operator preceedence precedence rules! If you want to drag 1235kg with your 22.90 body strength, you could carry 36.80kg = 22.90BS * 7 - 1235kg / 10 additional weight on your body and inventory.
Here's a small table of required minimum body strength for draggable items without any cargo.