Hammer price and buyer's premium
Two houses report $1,250 and $1,170 for the same wine. Both may have had a hammer price of $1,000. Here is how a published result breaks down, and why LastHammer shows the hammer price per bottle.
Two numbers for one sale
The hammer price is what the winning bidder bid: the number the auctioneer's hammer falls on, or the closing bid in an online sale. It is the market's answer to what the lot was worth that day.
The buyer's premium is the house's fee on top, a percentage of the hammer price. It runs from 10% at K&L to 25% at Zachys, Acker and Christie's. The buyer pays it, so the buyer's total is the hammer price plus the premium (plus tax and shipping).
The arithmetic
At a house with a 25% premium, a published result of $1,250 means a hammer price of $1,000 ($1,250 divided by 1.25). At a house with a 17% premium, $1,170 is also a $1,000 hammer price. A lot of six bottles with a $1,000 hammer price is $166.67 a bottle. A magnum holds two bottles' worth, so a magnum at $400 is $200 per 750 ml. That last step, the price per 750 ml bottle, is what lets you compare a case at one house with a single bottle at another.
Why it matters when you bid
When you look at a live catalogue, the question is always the same: is this lot cheap? The honest comparison is between the hammer price you are about to bid and the last hammer price for the same wine and vintage, at any house. The extension shows that number under the lot title. Click it to see the sales it came from, so you can tell whether the last price was one lot or ten. A link there takes you to the wine's page on CellarTracker for its most recent tasting notes.