Put 1 cup of sugar and 1 cup of water in a small pot. Heat the mixture until the sugar has dissolved.
Cut 6 lemons in half. Squeeze the lemons until you get 1 cup of lemon juice.
Pour the lemon juice, 3 cups of water, and 1 cup of cranberry juice into a pitcher. Add the sugar mixture, stir, and chill.
Notes
Refrigerator: Keep cranberry lemonade in a covered pitcher in the fridge for up to 5 days. Stir before pouring, since it settles as it sits.Make ahead: Make the simple syrup up to a week ahead and keep it chilled, or mix the whole pitcher the night before your gathering and keep it in the refrigerator.Ice cubes: Freeze some of the lemonade in an ice cube tray so your drinks stay cold without watering down.