Add all of the ingredients to a saucepan and mix together.
1 28 oz can crushed or petite diced tomatoes, 1/4 cup water, 1/3 cup sugar, 1/3 cup distilled white vinegar, 1 teaspoon salt, 1/2 teaspoon onion powder, 1/2 teaspoon garlic powder, 1/4 teaspoon black pepper
Bring the mixture to a boil.
Reduce the heat and let the ketchup simmer for 40-45 minutes while stirring occasionally, until it's thick and has cooked down by about half.
Use a stick blender, food processor, or standing blender to puree the ketchup until it is smooth. If the ketchup is too thin, return it to the heat until it's the desired thickness.
Let the ketchup cool and store in the fridge until you're ready to eat it.
Notes
Leftovers can be stored in an airtight container in the fridge for at least a month, or in the freezer for 4 months.
If you want to make the ketchup smoother, pass it through a strainer lined with cheesecloth.