Depending on where you live and how cold outside, you may be surprised at how much humidification is needed. I live on the north shore of Lake Superior in an older house that certainly is not well sealed, so there is significant exchange of inside and outside air. Take outside air at -20C (that's 4 below F) and warm it up to 22C (71.6K) and it is VERY low in Relative Humidity. For a whole house full of air, you cannot possibly add enough water vapour using only a single humidifier plugged into the wall in the living room. The only way to get there is to have a "power humidifier" installed in the furnace. Typically they use a small motor to rotate a foam drum through a water trough (fed by connection to the water pipes through a control valve) and then pass some of the hot air from the furnace output over it to evaporate the water and mix it back into the furnace air flow. These designs can evaporate water fast enough to keep inside room Relative Humidity in the 20 to 35% range in cold winter weather. Usually these units are installed with a humidistat (a control unit) mounted on the wall right next to your thermostat, and this can control how much water is added to the house air. A Relative Humidity gauge (ofter a desktop unit like a thermometer) can tell you whether you're getting the right results.
As others have posted, you generally do NOT try to keep the same indoor RH no matter what the outside temperature. The main reason is condensation on poorly-insulated surfaces like windows and door frames. These surfaces are colder than the rest of the house, so that high air RH will result in condensation or frost on them, leading eventually to mold and rot. So you keep the RH lower inside when the temp outside is too cold, to avoid that.