There is no absolute "fixed quantity" limit for container shipping in the United States. The actual loading volume mainly depends on the thickness of the clothing, the packaging method, and the billing volume (CBM). Generally speaking, approximately 1 cubic meter (1 CBM) of container space can accommodate the following number of pieces of clothing: 
*   Lightweight clothing: Such as folded pure cotton T-shirts, approximately 800 - 1000 pieces.
•  Regular clothing: Such as lightweight sweatshirts and shirts, approximately 300 - 400 pieces. 
Thick clothing items: Such as down jackets and thick coats. Due to their high level of fluffiness, they can usually only hold about 100 to 150 pieces. 
Key limiting factors 
Although theoretically you can fit many items as long as the volume permits, in actual operation you need to be aware of the following limitations: 
1. Billing Rules (W/M): The freight for consolidated shipments is usually calculated based on "the larger of volume and weight" (the general conversion standard is 1 CBM = 1000 KG). If your clothes are packed in a compressed manner (with high density), they may be charged by weight, resulting in an increase in freight.
2. Limitations on single-box operation: To facilitate loading and unloading and avoid damage to the goods, it is recommended to keep the weight of each box within 22 kilograms. Some logistics channels will charge additional handling fees for single shipments exceeding 25 items or items exceeding the weight limit per piece.
3. Packaging form: Using vacuum compression bags can significantly increase the number of loaded items (especially for down jackets), but be aware of the recovery time to avoid damaging the fibers. 
If you can provide the specific types of clothing and the estimated shipping volume (CBM), I can help you calculate a more accurate quantity.