I am confusing about some data for calculus.

First, the equivalence of weight: 1kgf=9.8N

Second, the mass of 1 Newton is: 1N/(9.8m/s$^2$).

And finally, to get the mass of 1kgf, I have to divide by the gravity.

An example of a weight of P=10N:

P=10N$\cfrac{\text{1kgf}}{9.8N}\approx1$kgf; its mass: $m=\cfrac{P}{g}=\cfrac{1kgf}{9.8m/s^2}\approx0.1kg$

While, directly from Newtons: $m=\cfrac{10N}{9.8m/s^2}\approx1kg$

What I am doing wrong?

  • $\begingroup$ It's the units. Dividing $kgf$ by $m/s^2$ doesn't give you $kg$. $\endgroup$ Aug 4, 2016 at 23:15
  • $\begingroup$ I am confused. What happened if I weight 70 kg, I must say 70kgf? I mean, to get my mass, I have to divide my weight by the gravity. What is wrong? $\endgroup$
    – Isai
    Aug 4, 2016 at 23:28
  • $\begingroup$ OK, how about if I tell you that gravity is $1 kgf / kg$. Does that help? $\endgroup$ Aug 4, 2016 at 23:31

1 Answer 1


Pay attention to the units. There is no such unit in the SI system as kgf. kg is mass, in kilograms. Force is Newtons. Acceleration is m/s^2. The three variables are tied together with Newton's 2nd Law, which is F=ma.

Having said that, weight is the force that gravity exerts on an object, and is defined by the equation W=mg, where W takes the place of F, and g takes the place of a, in Newton's 2nd Law.

Now, in case I haven't answered the question, take the units of g, and multiply them by kg/kg, which gives an answer of g=9.8kg-m/(s^2-kg). Since a Newton has units of kg-m/s^2 (from the units of F=ma), this means that g also has units of N/kg. So, from your last calculation, solving Newton's 2nd Law for mass yields m=F/a, which for a 1 kg mass yields 9.8N/(9.8N/kg).

  • $\begingroup$ Yes, thanks. I found this in Wikipedia: $1 kp=1 kgf=g_n⋅(1 kg)$. So, in my problem, I must say: $m=\cfrac{P}{g_n}=\cfrac{1 kgf}{g_n}=\cfrac{1 ·g_n⋅(1 kg)}{g_n}=1 kg$ $\endgroup$
    – Isai
    Aug 5, 2016 at 15:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.