Plastic Products and Mold Design

If You mean clamping force, it is F=A*p. F= reactive force, A = projected areas of cavities and runner system and p = the cavity pressure. Depending on material and part the cavity pressure is between 20 to 100 MPa, proper processing assumed.

More information on mold making: Menges& Mohren, How to make injection Molds, Hanser Publishers.

The product thickness has an important role in this formula as well. The thinner the product is, more pressure is necessary to fill the cavities, and more force is necessary to keep the mold closed.

But if you mean the mold weight, a simple approximation is to multiply width, lenght and height, times 7.85 (specific steel weight).

Thank You for giving response. Cavity pressure is most important for calculating clamping force, but it depends on type of plastic, wall thickness of product, injection pressure, temperature etc . Since you have write cavity pressure is between 20 to 100 MPa, Have you any chart about cavity pressure in which condition what cavity pressure is to be taken for clamping force calculation.