Markdown to PDF Converstion with Pandoc: Make pages a specific size, in inches

So I know you can use pagesize and geometry to set the page size of the PDFs Pandoc makes to presets (like a5, b5, etc), but is there a way to set a precise pair of dimensions? I'm going to be using the PDF with Amazon Self-Publishing (paperback) and I need the pages to be exactly 5x8in, as that's the closest setting KDP has to what I want. Thank you!