What should I list it for?

Add up what the item cost you and what you will pay to ship it, then find the price where the payout after eBay's fees covers those costs plus the profit you want. eBay's fees are a percentage of the whole order plus a per-order fee, so the price has to cover the fees on itself too. The calculator does that math and gives the lowest price that meets your goal.

Margin is profit as a share of what the buyer pays you: a $30 sale with $9 profit is a 30% margin. Return on cost is profit as a share of what you paid for the item: $9 profit on a $6 item is a 150% return. Margin can never reach 100%, because fees and costs always take part of the sale; return on cost can go well past 100%.

eBay's fees grow with the price, so the share of each sale you keep has a ceiling. With a 13.6% final value fee, no price can give you an 87% margin or more, and promoted listings and sales tax lower that ceiling further. Aim for a dollar profit instead, or a lower margin.

eBay charges its fee on the shipping the buyer pays as well as the item price, so the fees come out about the same either way. Choose free shipping, calculated shipping (the buyer pays the postage), or a flat shipping charge, and the calculator raises or lowers the item price to match. Box and packing supplies are always your cost, so enter them separately.

It shows the exact lowest price that meets your goal, and by default rounds it up to the next price ending in .99, which never falls below that minimum. Turn rounding off to list at the exact minimum.