Question

how are the units of weight, kgf and newton related

Answer 1

The deprecated unit kilogram-force (kgf) or kilopond (kp) is the force exerted by one kilogram of mass in standard Earth gravity (defined as exactly 9.80665 m/s²). One kilogram-force is equal to exactly 9.80665 newtons.

Answer 2

because SI unit of weight is kg
mass also has same SI unit. .ie..kg

the formula to calculate force =Ma
where m is mass and a is acceleration
Si unit of mass =kg
si unit of acceleration =m/s^2
there fore si unit of force is kgm/s^2