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Calcimator

Shot Size Calculator

Calculate barrel capacity needed from part weight, runner volume, number of cavities, and cushion percentage.

Inputs

oz
oz
%

Results

Required Shot Size

170.5 g

≈ 2 sticks of butter

Total Part Weight140 g
Shot Weight (no cushion)155 g
Shot Volume (approx)162.38 cm³
Min Barrel Capacity213.13 g
Ideal Barrel Capacity341 g
Runner Percentage9.7%
Max Barrel Capacity852.5
Barrel Utilization50%
How to Use This Calculator
  1. Enter part weight (g), number of cavities, and estimated runner/sprue weight (g).
  2. Set cushion percentage (typically 10–15% of barrel capacity) to maintain pack pressure.
  3. Review required shot size with cushion, total shot weight, shot volume (cc), and minimum barrel capacity.
  4. Select an injection molding machine whose barrel capacity is 30–80% of your shot size for optimal plasticizing.

How the result changes with Part Weight

Part WeightRequired Shot Size
5,00022,016.5 g
17,50077,016.5 g
32,500143,016.5 g
45,000198,016.5 g

What each input means

Part Weight
Weight of a single finished part in grams.
Number of Cavities
Number of cavities in the mold.
Runner / Sprue Weight
Total weight of the cold runner and sprue system (0 for hot runner).
Cushion
Cushion as percentage of shot (typically 5-10% for consistent packing).

What each result means

Min Barrel Capacity
Barrel capacity where shot is 80% (maximum fill).
Ideal Barrel Capacity
Barrel capacity where shot is 50% (optimal residence time).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Part Weight = 35, Number of Cavities = 4, Runner / Sprue Weight = 15, Cushion = 10 = 4 input(s) provided
  2. Calculate Required Shot Size
    Required Shot Size
    170.5 = 170.5
  3. Calculate Total Part Weight
    Total Part Weight
    140 = 140
  4. Calculate Shot Weight
    Shot Weight
    155 = 155

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

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