MPA stands for megapascals, a unit of pressure. A kilonewton, abbreviated kN, is a unit of force. However, by combining kilonewtons with a unit of area, such as millimetres squared (to get kN per mm^2), you have a unit of pressure. If you need to inflate an object, such as a car tire or air bed, you can use it to make sure you have the right pressure: you may have to convert from one unit to another by hand.
Multiply the number of MPA by 0.001^2 kN/mm^2 per MPA to convert to kN/mm^2. For example, if you had 23 MPA, you would multiply 23 MPA by 0.001 kN/mm^2 per MPA to get 0.023 kN/mm^2.
Divide the number of MPA by 1,000 MPA per kN/mm^2 to convert to kN/mm^2. For example, if you had 23 MPA, you would divide 23 MPA by 1,000 MPA per kN/mm^2 to get 0.023 kN/mm^2.
Confirm your answer using an online pressure units conversion calculator.