# I Want to Drink Your Blood. I'll Need 6.4 Minutes

The feverish pace of modern life makes it difficult to fit everything in — and that includes slotting time for your vampire master to periodically drink your precious blood. Now, thanks to a paper published in Journal of Physics Special Topics, you know exactly how long your beloved bloodsucker needs to guzzle your plasma.

Here's how the four researchers from the University of Leicester figured it out. First, they decided on the amount of blood consumed in a given blood feast. Since your vampire is a loving master, he wouldn't want to take more blood than you can healthily give. Based on information from the American College of Surgeons' Advanced Trauma Life Support program, the researchers figured that amount at 15 percent of your blood volume — technically a "class 1 hemorrhage." Don't let your vampire overlord talk you into a class 2 unless he's willing to make good on his promise to turn you.

Just how long does it take to drink 15 percent of a person's blood? This is where the English research team busted out the math. First of all, they decided to go with the bat-model of blood drinking: free-flowing lapping rather than sucking from a pair of 0.5-millimeter neck punctures. They calculated the average diameter of the aorta and the five connected arteries, as well as the pressure and the heart-driving velocity of the flowing blood.

A few equations later, the researchers determined that any self-respecting vampire needs 6.4 minutes to drain a polite 0.75 liters (0.79 quarts) of blood from his or her thrall. To put that in perspective, it takes less than an hour to give 0.47 liters (0.50 quarts) during a blood drive, where they tend to take 8-10 percent (and drink virtually none of it).

The researchers indicate that more work can be done to determine the mealtimes for class 2 and greater feedings. They also stress that vamps could "reduce the time taken and make the process more efficient" by applying a little suckage.

So if 6.4 minutes is still too long, talk to your favorite vampire about his feeding technique.