The weight capacity of typical shelf brackets can vary significantly based on several factors, including the material, size, design, and installation method. Generally, standard shelf brackets are made from materials such as steel, aluminum, or plastic, each offering different levels of strength and durability.
1. **Material**: 
   - **Steel Brackets**: These are the most common and can support a wide range of weights. Light-duty steel brackets might support around 20-50 pounds per pair, while heavy-duty options can hold up to 500 pounds or more.
   - **Aluminum Brackets**: Typically lighter than steel, aluminum brackets are often used for medium-duty applications, supporting around 50-200 pounds per pair.
   - **Plastic Brackets**: These are generally used for light-duty purposes, supporting around 10-50 pounds per pair.
2. **Size and Design**: 
   - Larger brackets with more surface area and additional support features (like gussets) can hold more weight. For example, a 12-inch bracket will generally support more weight than an 8-inch bracket.
   - Designs such as L-brackets, Z-brackets, or those with diagonal supports can also influence weight capacity.
3. **Installation**: 
   - Proper installation is crucial. Brackets must be securely attached to wall studs or appropriate anchors. The type of wall (drywall, concrete, etc.) and the quality of the fasteners used can significantly affect the weight capacity.
   - Even the strongest bracket will fail if not properly installed.
4. **Spacing**: 
   - The distance between brackets also affects capacity. Closer spacing generally increases the overall weight the shelf can support.
In summary, while typical shelf brackets can support anywhere from 10 to 500 pounds, it is essential to consider the specific bracket type, material, and installation method to determine the exact weight capacity for your needs.