Gating Ratio Calculator

The Gating Ratio Calculator is a specialized tool used in metal casting design. It helps engineers and foundry technicians determine the ideal ratio between the sprue, runner, and ingate areas in a gating system. This ensures a smooth and controlled flow of molten metal into the mold cavity, reducing turbulence, air entrapment, and casting defects.

By calculating an optimized gating ratio, users can enhance casting quality, reduce waste, and improve mold filling efficiency. The tool also supports decision-making when switching between pressurized and non-pressurized gating systems, depending on the type of metal being cast.

The Gating Ratio Calculator belongs to the “Industrial & Engineering Calculator” category.

Formula

1. Gating Ratio Formula

Gating Ratio = Sprue Area : Runner Area : Ingate Area
This ratio is written in simplified form as:
As : Ar : Ai_total

Where:
As = Cross-sectional area of the sprue
Ar = Cross-sectional area of the runner
Ai_total = Total cross-sectional area of all ingates
Ai_total = Ai × number_of_ingates

2. Cross-Sectional Area Formula (for Circular or Rectangular Sections)

For circular cross-section:
A = π × (D / 2)²
Where:
A = Area
D = Diameter
π ≈ 3.1416

For rectangular cross-section:
A = width × height

These formulas apply to sprue, runner, and ingates depending on their shape.

3. Types of Gating Ratios (Based on Metal Type)

Here are some common gating ratios used in foundries:

• Aluminum (pressurized): 1 : 2 : 2
• Steel (non-pressurized): 1 : 2 : 4
• Grey Cast Iron (non-pressurized): 1 : 2 : 4 or 1 : 3 : 3
• Brass/Bronze (pressurized): 1 : 1.5 : 1.5

These are target values to guide the design. The calculator can help you check how close your current system is to these ideal ratios.

4. How to Calculate Gating Ratio

Step 1 – Measure or input the dimensions (diameter or width × height) of the sprue, runner, and ingates.
Step 2 – Use the formulas to calculate each area:

• For circular: A = π × (D / 2)²
• For rectangular: A = width × height

Step 3 – Calculate the total ingate area:
Ai_total = Ai × number_of_ingates

Step 4 – Plug values into the gating ratio:
Gating Ratio = As : Ar : Ai_total

Step 5 – Normalize the ratio by dividing all parts by As (sprue area):
Normalized Ratio = 1 : (Ar / As) : (Ai_total / As)

This gives a clearer picture of how the gating system is balanced relative to the sprue.

Gating Ratio Reference Table for Common Cases

This table provides approximate area values and corresponding normalized ratios to help users avoid manual calculation in common scenarios.

Sprue Ø (mm)	Runner Ø (mm)	2 Ingates Ø (mm each)	Ratio (As : Ar : Ai_total)	Normalized
20	28	16	314 : 616 : 402	1 : 1.96 : 1.28
25	35	20	491 : 962 : 628	1 : 1.96 : 1.28
30	40	22	707 : 1257 : 760	1 : 1.78 : 1.08
20	25	12	314 : 491 : 226	1 : 1.56 : 0.72

These are for circular cross-sections. Values are in mm², rounded.

Example

You have the following:

• Sprue diameter = 25 mm
• Runner width = 30 mm, height = 15 mm (rectangular)
• Two ingates, each 20 mm diameter

Step 1 – Calculate areas:
Sprue area = π × (25 / 2)² = 491 mm²
Runner area = 30 × 15 = 450 mm²
Ingate area (each) = π × (20 / 2)² = 314 mm²
Total ingate area = 2 × 314 = 628 mm²

Step 2 – Gating ratio:
Gating Ratio = 491 : 450 : 628

Step 3 – Normalize by dividing by 491:
Normalized Ratio = 1 : 0.92 : 1.28

This means the runner is slightly smaller, and the ingate area is larger than the sprue area. You may want to adjust dimensions for a more balanced or metal-specific design.

Most Common FAQs