I've been thinking about the bite force myth regarding so-called 'pit bull' dogs today.  You know, the one repeated in news reports about dogs having a bite force of 2,000 pounds per square inch?  This 'fact' is totally irrelevant in terms of dog bites, of course.  If I get hit by a Volkswagen or hit by a Hummer I'm still going to be hurt.  It's the guy behind the wheel I have to worry about, not the mechanism itself.  

In view of the nonexistence of the 'pit bull' breed, I guess one would have to test the purebreds commonly called 'pit bulls' separately and would of course be unable to test any mutts and put them into a category other than 'mixed breed' possibly sorted by weight.  This assumes the actual measurement is useful in the first place in terms of dog bite prevention.

I was reminded that I found a paper awhile ago on bite force in Alligator missississipiensis, the American Alligator, which is very technical but extremely interesting..

 

Update Aug 20:  I just found this articleabout the paper from 2003.

First of all, force is calculated in Newtons, a measurement of force defined as

Newton: In the meter-kilogram-second system, the unit of force required to accelerate a mass of one kilogram one meter per second, equal to 100,000 dynes." at Dictionary.com

Pounds/square inch is a unit of pressure, something rather different so it's really comparing strength to weight.  I'll make the assumption that if a creature exerts significant force they will exert significant pressure with their jaws and if not, then not.

The measurement in alligators was at the tooth, here's an excerpt:

"The appropriate transducer was then placed unilaterally between the jaws and centred both mesio-distally and labio-lingually at the apex of the 11th maxillary tooth, the most prominent tooth at the back of the jaws."

There are approximately 4.45 N/lb, so to calculate the alligator's bite force in pound force, we would do this:

9200/4.45 = 2,067.42 (rounded) 

Therefore an alligator has a tooth-tip bite strength of roughly 2,000 pound-force.  Area is not a factor in calculating force.

Here's a Table from the Alligator paper showing comparative bite force (not pressure) in various animals measured in Newtons (N). 

I know this is a bit hard to read but I wanted to show the graph.  I added the vertical line which bisects the 0-2000 N column to make it easier to see where humans, sharks, etc lie.   Here is the list of animals on the left side of the table:

Tyrannosaurus rex † (giant theropod dinosaur)

Allosaurus fragilis † (large theropod dinosaur)

Alligator mississippiensis (crocodilian)

Crocuta crocuta (spotted hyena)

Panthera leo (African lion)

Pongo pygmaeus (orangutan)

Carcharhinus obscurus (dusky shark)

Canis lupus (grey wolf)

Homo sapiens (human)

Canis familiaris (labrador dog)

And here is the text underneath the chart, emphasis mine:

Fig. 6. Comparison of Alligator mississippiensis biting forces with some the largest values in the literature for other gnathostomes. These data include empirical measures of maximal biting force made using bite bars and theoretical measures using various modelling techniques (Snodgrass & Gilbert, 1967; Dechow & Carlson, 1983; Thomason, 1991; Strom & Holm, 1992; Binder & Van Valkenburgh, 2000). The data for Tyrannosaurus rex are derived from simulations of a single tooth mark that were probably made during sub-maximal biting and thus are considered conservative (Erickson et al., 1996). Note that A. mississippiensis bite forces are the highest known for any living taxon and are much higher than those for the 1.4-ton Allosaurus. This suggests that crocodilians have relatively higher bite forces than theropod dinosaurs.

I am not a scientist and admit to never being good at physics but I want to figure this out.  I'm using this converter, which is handy.

Just for comparison let's look at a couple of examples from the list, estimated from the bars for the N and rounded for the pf

                                    Newtons                    Pound-Force

Alligator                           9200                              2067

African Lion                     4100                                922 

Grey Wolf:                      1500                                 337

Human                              750                                 168

Labrador dog                    750                                 168

 

The bar graph to me tells it all.  Alligators have a bite force of approximately 2,000 pounds.  I have no idea how to convert that to psi. 

Anyone interested in physics, please leave a comment if you know how to convert the values.

Conversion aside, does it sound reasonable that dogs would have a bite force equal to an alligator? 

The best part about the chart?  Dogs are right next to humans, where they should be.

 

Notes:

I am aware of only one attempt to measure bite force in domestic dogs which was unsuccessful.  Here is the abstract from the pilot study:
MEASUREMENT OF BITE FORCE IN DOGS: A PILOT STUDY
Donna L. Lindner, DVM; Sandra Manfra Marretta, DVM; Gerald J. Pijanowski, DVM; Ann L. Johnson, DVM; Charles W. Smith, DVM

Summary: A force tranducer was developed to measure bite force in dogs. A total of 101 readings was obtained from 22 pet dogs ranging in size from 7 to 55 kg. Bite forces ranged from 13 to 1394 Newtons with a mean for all dogs of 256 Newtons and a median of 163 Newtons. Most measurements fell within the low end of the range, with 55% of the biting episodes less than 200 Newtons and 77% less than 400 Newtons. J Vet Dent 12(2):49-52, 1995.

Here's the reference for the alligator study:

The ontogeny of bite-force performance in American alligator (Alligator mississippiensis)  Gregory M. Erickson*, A. Kristopher Lappin and Kent A. Vliet  J. Zool., Lond. (2003) 260, 317–327

UPDATE II July 25

My friend Alan, who actually IS a scientist, kindly sent this note along:

"A newton equals 0.2248 pound force, which is the force a one pound weight would exert on whatever it is resting on on Earth.  Thus 12 newtons = 2.7 pound weight equivalent, and 9452 newtons is equivalent to 2125 pounds of pressure exertion on an object.   A newton does not distinguish the area of the force it is exerting on, ie 12 newtons or 2.7 pounds if it was pushing against a square inch, then it would be 2.7 pounds per square inch, but if it was an exertion on 12 square inches, then it woud be 2.7 pounds per square foot. It was interesting to see in the article that human and lab dog have about the same bite force, and wolves only have about 2.5 times more bite force than humans.
 
Alan"
OK, so let's try the highest number obtained in the Lindner study, 1394 N:

1394 x .2248 = 313  pound force (rounded).

As another reader, who also happens to be my brother the race car driver, put it:

"Forget the science.  To combat bulls--t, use this:

If I measure the area (not volume)  inside a dog's mouth and say it's a really big dog and the area is 4" x 6", I get 24 square inches.  If a dog's jaws are capable of exerting a pressure of 2,000 psi, that means this dog is capable of exerting a force of 48,000 pounds with his mouth. Sound believable?  No, it doesn't because the frame of reference for this made-up 'fact' is probably supposed to be inferred as the tooth, which changes the theory quite a bit, ie, it is only on that tooth tip that the pressure is exerted, not across the area.

If a woman weighs 100 lbs and wears a stiletto heel and stands on it, she may exert a force of 100 lbs/.25 square inch, correct?  So the pressure would be 400lbs/square inch.  If she wears snowshoes or lies flat on the ice, she will exert far less pressure.

See?"

I think so.  Thanks, brud!

To convert Newtons to pound-force to psi, see this article.