Sell Through Rate:
Listing sold / Number of listing = Sell through rate
100 Listings, 40 listings Sold
40 / 100 = 0.4 or a 40% sell through rate
Number of items sold per listing:
The formula is similar to the sell through rate and is:
Number of items sold / Number of listing = Number of items sold per listing
100 Listing, 55 total items sold
55 / 100 = .55 items sold for every listing.
You could also view this as a percentage of 55% to make it identical to the sell through rate.
You would want to track because a item with a sub par sell through rate of say 25% would still be doing well if this number is high. For example .45 items sold per listings is roughly equivalent of a 45% sell through rate.
Gross margin as a percentage:
(Sale price - Cost) / Sale price = Gross margin
$9.95 sale price, $5.50 Cost
($9.95 - $5.5) / $9.95 = 44.72% Gross margin
Gross Margin in actual dollars:
Sales Price - Cost = Gross margin
$9.95 - $5.50 = $4.45 gross margin
Using Gross Margin Percentage To Figure Sales Price:
Cost / (1 - Gross Margin Percentage) = Selling Price
Filling in the numbers you get
$5.00 / (1 - .6) = $12.50. So in this example you would need to sell the item for $12.50 in order to have a gross margin of 60%.
eBay Fees As A Percentage Of Sales:
eBay Fees / Sales = Percentage of sales you are paying to eBay.
$800 in sales, $64 in eBay fees
$64 / $800 = 8%
Cost Per Conversion:
Fees / Number of sales = Cost per conversion
100 Listing, 55 sales, $64 in fees
64 / 55 = $1.16 cost per conversion.
Unfortunately I can't tell you exactly what to do with these numbers as they will mean different things to every business. In general you are looking for fluctuations in the numbers that may indicate business is slowing (or growing) or becoming less (or more) profitable so you can take appropriate action.
You can find eBay Cost Per Conversion and a eBay / Website profit calculator Excel spread sheets on my eBay About Me Page .