It's the biggest nest box I have ever built. 23 inches tall ... 9 inches square. The ducks have been in the pond for 2 days in a row looking for a nesting site. The cedar plank box is now on a pole 3 feet above the water waiting for residents. That's a standard blue bird box I built to the left for a size comparison.

UPDATE.. It's April 24th the ducks have been here on and off everyday since I set box. I think she has started laying her clutch of eggs?