How to Check Proper Humidity in a House

Create a controlled environment to calibrate your hygrometer by adding 1/2 cup salt and 1/4 cup water to a coffee mug. Stir with a spoon until the salt is mostly dissolved. Wipe the sides and bottom of the coffee mug with a paper towel if any water gets on the outside of the mug.

Open the zipper-seal bag and place the liquid-filled coffee mug inside. Place the hygrometer in the bag as well without getting the hygrometer wet.

Seal the plastic bag by sliding or squeezing the zip top closed completely.

Set the bag in a room with a constant temperature, out of direct sunlight, without spilling the contents of the mug. If your hygrometer is electronic, make sure it is on by pressing the "on" button through the bag, following manufacturer's instructions. Let the bag sit overnight or for 8 to 12 hours.

Note the hygrometer reading. If it reads anything other than 75 percent, adjust the hygrometer dial or indicator to 75 percent per the manufacturer's instructions. If your hygrometer is not adjustable, note the difference between the reading and 75 percent, so you can mentally adjust its reading later. Remove the items from the bag. Dump the cup's contents into the sink.

Place the hygrometer in a room other than the bathroom that seems overly damp or dry. If none of the rooms seems too damp or dry, set it somewhere near an indoor wall. Keep the hygrometer out of direct sunlight and away from heat or air conditioning sources such as heat registers, radiators or air conditioners.

Wait at least two hours, then read the hygrometer's dial or LED screen. Mentally adjust for differences if your hygrometer is not adjustable. For instance, if your hygrometer read 78 percent in Step 5, subtract 3 from the total percentage on the current readout. The display shows the relative humidity of your home.