Here are some rules of thumb that we share when helping a customer make their louveer size choice. How much volume does the room have? Do you have 8 foot ceilings or 16 foot ceilings? How big are the windows? Large with big views or smaller with obstructed views. How large is the trim in the and the baseboards? The larger the baseboards the larger you can make your louvers.
While there is no set rule for choosing a louver size, considering these sorts of proportions will help you decide if the bigger louver will be a pleasant design choice, or if a smaller louver will hit that sweet spot. For whatever it is worth, 80% of the homes we service choose the 3.5" louver, as it fits well with most of the homes you find in master planned communities. However, don't be afraid to venture to the 2.5" or 4.5" option, as they can really work well - especially if you are considering your design preferences and proportions.
We would love to help you with your next plantation shutter project. For a quick idea of what your project might cost, check out our online shutter cost calculator.