CompuServe Messages

I have created a 3D Studio image which a local bureau will print for me as a high resolution A4 (8 1/4" x 11 1/2") size photograph. The bureau cannot read 3D Studio files but can read a variety of file formats through Adobe Photoshop. If I take my rendered image into Photoshop, to create a file format that they can read, and set the image output resolution to 300 dots per inch, the image size changes and does not fill an A4 page size. Does anyone know what resolution I should render my 3D Studio image at to ensure that the printed image out of Adobe Photoshop, set at 300 dots per inch, will fill an A4 page? It may be easier for me to use a bureau that can read 3D Studio files! But any advice would be appreciated. Thanks.