The following information is based on your documents being A4 in size and packed tightly. Variations will depend on the sizes and quantity of documents that are double sided.
A four drawer filing cabinet normally holds 3,000 pages per drawer or 12,000 pages when full.
A normal archive box will hold around 2500 pages when full.
A normal small archive box will hold around 500 pages when full.
A normal A4 Lever Arch Folder will hold around 300-400 pages when full.