Calculate injection pressure, force, or projected area from any two values using lb, N, kgf, in², ft², cm², m², psi, bar, kPa, or Pa.

Injection Pressure Calculator

Enter any 2 values to calculate the missing variable

Related Calculators

Injection Pressure Formula

IP=\frac{F}{PA}

Variables:

  • IP is the (average) injection pressure (psi)
  • F is the force (lbf)
  • PA is the projected area (in²)

To calculate injection pressure (average pressure over the projected area), divide the force by the projected area.

How to Calculate Injection Pressure?

The following steps outline how to calculate the Injection Pressure.

  1. First, determine the force (lbf). 
  2. Next, determine the projected area (in²). 
  3. Next, gather the formula from above = IP = F/PA.
  4. Finally, calculate the Injection Pressure.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

force (lbf) = 500,000

projected area (in²) = 100

Injection Pressure: IP = F ÷ PA = 500,000 ÷ 100 = 5,000 psi

FAQs

What is injection pressure and why is it important in injection molding?

In injection molding, “injection pressure” commonly refers to the pressure used to drive molten material through the nozzle/gate and into the cavity (often discussed as plastic/melt pressure or cavity pressure). It’s important because it affects filling, packing, part quality, and defects. This calculator specifically computes the average pressure implied by a force distributed over a projected area using P = F/A.

How does the projected area affect the injection pressure calculation?

In this calculator, the pressure is inversely proportional to projected area: for the same force, a larger projected area produces a lower average pressure (P = F/A). In injection molding practice, projected area is most often used the other way around: for a given cavity pressure, a larger projected area requires a higher clamp force (tonnage) to keep the mold closed.

Can the injection pressure be too high? What are the consequences?

Yes. Excessive injection or cavity pressure can lead to issues such as flash (material escaping at the parting line), high residual stresses/warpage, and potential mold or machine wear/damage. Pressure should be optimized along with temperature, speed, and packing/holding settings.