Just roll the wheelbarrow right over an in-floor scale! Subtract the wheelbarrow's own weight, which can be printed on the wheelbarrow itself. Or for something

Just roll the wheelbarrow right over an in-floor scale! Subtract the wheelbarrow's own weight, which can be printed on the wheelbarrow itself. Or for something more high tech, put a QR code on the wheelbarrow and you can periodically update its empty weight in the database when it's empty and scan it at checkout. This is basically how it works at my local landscaping store where they sell gravel by weight.