Quarter-inch hexagon paper
Quarter-inch hexes, small enough to fit a continent on one sheet, too small for miniatures. A campaign-map scale rather than a battle-map one.
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Two different jobs, two different hex sizes
Tabletop hex grids split cleanly by purpose. One-inch hexes are for tactical play with miniatures on the table, sized so a standard base sits inside a cell. Quarter-inch hexes are for overland and campaign maps, where each hex is some distance of travel, six miles is the traditional choice, inherited from early hex-crawl design, and what matters is fitting a whole region on one page. Printing the wrong one is the difference between a map you can play on and a map you have to redraw.
How many you actually get
At quarter-inch hexes a US Letter sheet holds roughly 35 across and 54 down inside sensible margins, which is a little under 1,900 cells. At six miles per hex that is a region about 210 by 320 miles, most of a small country, or a comfortable campaign area with room at the edges for the parts you have not invented yet.
Numbering, and doing it before you draw
Hex maps get referenced constantly in play, and a map without coordinates means describing locations by landmark, which falls apart as soon as two places look similar. The usual convention is a four-digit reference: column then row, so 0312 is column 3, row 12. Write the column numbers along the top edge and rows down the side before you start drawing terrain, because adding them afterwards means working around whatever you have already put in the margins.
Printing it accurately
This only measures correctly if your printer doesn't rescale the page. In the print dialog set Scale: 100%, not "Fit to page" or "Shrink oversized pages". If you're not sure it worked, print the calibration page, measure the ruler on it with a real ruler, and it will tell you exactly what your printer is doing to the page.