Wash, dry, and mash your raspberries in a large bowl. Keep track of how many raspberries you have to adapt the recipe as needed.
Add the mashed raspberries and lemon juice to a dutch oven or stock pot. Add the sugar and sprinkle the pectin on top.
Heat the mixture over medium heat and stir occasionally. Skim off any foam from the top of your jam.
As the jam is cooking, fill up your tall stock pot with water to boil. Set up a small pot with water over medium on a back burner and simmer your new lids and rings for 10 minutes. Sanitize your jars by boiling them in water for 10 minutes.
Cook until the mixture starts to thicken. To test if the jam has set, scoop a small amount of jam onto a cold saucer (or stick it in the freezer for a minute). Run your finger through the center of the jam. If your finger leaves a clean trail and the jam stays on either side of the divide, it's ready.
Set your sanitized jars on a clean towel. Add your canning funnel to a clean jar and pour in enough jam to fill the jar except leave 1/4 inch for headspace. Use your headspace measuring tool to make sure your pour was accurate. Continue filling your jars until you've used all of the jam. With a wet, clean towel, wipe off all the rims of the jars to make sure there is no residue that could disturb the seal.
Remove the jar lids from the small pot where they were simmering. Dry them off and place them on the jars. Close with a band. Tighten the lids as well as you can.
Add the jars to your tall stock pot or boiling-water canner. Make sure there is something between the bottom of the jars and the pan like a metal rack or kitchen towel.
Add enough water to cover the top of the jars with at least one inch of water. Turn up the heat until the water begins to boil.
Once the water is boiling, set a timer for 10 minutes. If you live above sea level, you will need to add more time based on your area. This timing is meant for half-pint jars only. You will need to process the jam longer if you use larger jars.
When 10 minutes are up, turn down the heat and allow the jars to sit in the pot for about 5 minutes. Then remove them to a clean, dry towel on the counter.
If you were not able to fit all of your jars in your first round of canning, run the next round following the same instructions.
Leave them to cool completely for 12-24 hours. After that time, remove the bands from the jars. Test your seal by pressing on the center of the jar. It should stay down when pressed.
How to tell if your jam is ready for canning:
The gel test: Scoop a small amount of jam onto a cold saucer (or stick it in the freezer for a minute). Run your finger through the center of the jam. If your finger leaves a clean trail and the jam stays on either side of the divide, it's ready.
The wrinkle test: On the same plate, tilt the plate sideways. When the jam starts to move down with gravity, wrinkles should appear on the surface of the jam.
Be sure to process half pint jars for 10 minutes in a boiling water bath canner. Add an extra minute for every 1,000 feet above sea level.