What is the difference between ft pounds and in pounds in torque wrenches How many inch pounds are in ft pounds or vise versa?

Ft-Lbs is a measurement of torque. Torque is "twisting" force.

Ft-Lbs is measured as follows: Imagine a 1 ft bar attached at some center point. The bar is horizontal and a 100 lb weight is attached to the bar at one foot from the center point. That would be the very definition of 100 ft-lb of torque. Of course for this to be accurate you'd have to account for the weight of the bar. In this instance 100 ft pounds of torque would mean that a 100 pound weight was used instead. You could also use a 100 ft bar and ONE pound weight, the theoretical results would be identical.

Inch pounds are very similar, only the bar would be one inch long. To calculate 100 inch pounds you'd have a bar that was 1 inch long, at the horizontal and hang a 100 pound weight. For all practical purposes 100 inch pounds would be 1/12 of the torque represented by 100 Ft pounds.

In other words, there are 12 inch lbs, in one ft. lb.

An easy way to think of it is based on the unit of measure. Whether you are working with Ft-Lbs or In-Lbs or even in Metric using N-M (Newton-Meters) doesn't matter.

If you were to express Ft-Lbs as "Pounds per Foot" or In-Lbs as "Pounds per Inch", or in metric "Newtons of force per Meter" it may be easier to understand.

For conversion purposes, there are 12 inches in a foot, so "one foot pound" would equal "Twelve Inch Pounds". In other words, it takes "12 pounds of force on a one inch long bar" to equal the twisting force of "One pound of force on a one foot (12 inch) long bar"