What you need: Freshly ground coffee, a kitchen scale, a coffee grinder, a large jar, a spoon, and cheesecloth (or some other means of straining coffee).
What you do: Use scale to measure out coffee and water. A good ratio of coffee to water for cold brew is 1 to 4, and since we’re going to be making 16oz of cold brew, we’ll be using 4oz of coffee, or around 120g of coffee to 470g of water for you metric folks.
Grind coffee to coarse grind setting. Similar to French press, but even coarser.
Add coffee to jar, and place on scale. Tare.
Add entire volume of water (in this case 12oz) to jar. Use spoon to stir and ensure even saturation of ground coffee. Seal jar and place in refrigerator for 12 hours.
When brewing is complete, use cheesecloth or another similar straining device to separate cold brew from ground coffee. Decant, dilute to taste or enjoy as is.