How to calculate how much weight you push up in a pushup? I put my hands on a scale in push-up position to see how much I was pushing up, and it came up to around 65-70% of my bodyweight. I find pushups a lot easier than benching 65-70% of my bodyweight in terms of the number of reps I can do. I was wondering why, and what the difference might be there? What is the weight-equivalent bench for a push up and why?
 A: Push ups are not equivalent to a bench press.  As you do a push up, the angle of your body with respect to the floor changes, resulting in a reduction in the amount of force that you have to exert as you rise higher off the floor.  For a bench press, you always have to push the bar vertically, which requires the same amount of force throughout the press.  This means that if you measure your push up force as you start the push up and use this amount of weight on the bench press, you are doing more work during the bench press than you are doing during a push up.
A: I don't know why pushing 70% of your bodyweight is different to benching it, but it would assume that it is purely some psychological thing. (i might be wrong here, feel free to correct me.)
But i do know how you can calculate the weight you push, when doing a pushup. At least aproximately. I will now assume, that you body is a rectangle, and that the weight is distrubuted equally throughout it. Also your arms have no mass now. A pushup with stretched arms can then be illustrated as below:

$L$ is the length of your body (your height), $h$ is the length of your arms.
We can now create a function, that shows how much work you have done on your body. Let the mass of your body be $m$. We can then split your pushup into two different positions, up and down position:

If we then want to calculate the work you have done on a single point on your body, it would look like this.

Where $m_i$ is the mass of the single point we are calculating. We can set set up and infinite sum (integral) to find the total energy needed to lift your entire body from Down to Up:
$ \int_{0}^{L} x\frac{h}{L}\cdot m_i\,dx$. if you assume the weight is evenly distrubuted, $m_i$ will be equal throughout the integral, and will just be the total mass, $m$. The integral can then be written as: $\frac{h}{L}\cdot m \int_{0}^{L} x\,dx=\frac{h}{L}\cdot m$
