Prepare jars or plastic containers by cleaning and drying them thoroughly.
Peel, pit, and mash or finely dice or chop peaches. See notes for the easiest way to peel peaches. Measure out exactly 3 cups and transfer to a large bowl.
3 cups mashed peaches
Add lemon juice and 2 1/2 cups of the sugar. Stir well, then let sit for 10 minutes. Add another 1 cup of sugar, stir, and let sit for another 10 minutes. Add the final 1 cup of sugar and stir well. Let sit for 10 minutes.
2 Tablespoons fresh lemon juice, 4 1/2 cups granulated sugar
Combine water and the pectin powder in a small saucepan. Bring to a boil over medium-high heat while stirring constantly. Boil for 1 minute while continuing to stir. Remove from the heat.
3/4 cup water, 1 box SURE-JELL fruit pectin
Pour the hot pectin liquid into the peach and sugar mixture. Stir for 3 minutes to dissolve sugar crystals and make sure the jam is evenly combined.
Transfer the jam to prepared containers, leaving 1/2-inch of space at the top of each jar or container so there is room for the jam to expand while freezing. Cover with lids and let sit at room temperature for 24 hours to set up.
Refrigerate for up to 3 weeks or transfer the jam to the freezer and freeze for up to 1 year. Thaw jam in the fridge overnight before enjoying.