This is a Quora question I was asked to answer.

You are going to generally size based on the competing products already available to consumers. The reason is because that is what consumers expect and in many cases, supply chain, warehousing, e-commerce operations and store shelves are already optimized for the sizing sold.

If you sell direct to consumer or via other online resellers, you want to try and maximize the order value, ideally above $75 in order to earn sufficient revenue to pay for the e-commerce operations. So you might bundle multiple units of your product together or create a special size that allows you to get that average order value up.

If you sell through club retailers, your size will be bigger automatically, which might be a special SKU for that channel/retailer or the multiple units sold as one item , since volume is what those retailers look to move.

So, in general, pick the size that consumers expect, and bundle as needed from there to sell direct-to-consumer, through online and club channels.