Decide what you want to achieve
Are you crafting for yourself, profession skill or resale? Each needs a different comparison. Personal use means comparing full crafting cost with the purchase price. Skill progression also depends on whether the recipe can still advance your profession.
Start with a simple recipe
A Bolt of Linen Cloth uses two Linen Cloth. Compare twice the cloth unit price with one bolt unit price. Enter your actual prices instead of copying an old gold figure from a guide.
Include every ingredient
Superior Mana Potion uses two Sungrass, two Blindweed and one Crystal Vial. The purchased vial costs money too. The recipe requires Alchemy260 and is learned from recipe item13477; the linked calculator opens that recipe.
Value materials you already own
For “what must I pay now?”, subtract owned ingredients from the shopping list. For “is crafting worthwhile?”, consider their alternative use. A gathered herb could be sold or used in a different recipe.
Divide by the actual output
Calculate the full craft first, then the cost of one finished item. Ingredient quantity is not output quantity. Include random extra products only when the relevant rule is reliably known.
A missing price leaves an incomplete total
Check the imported market and scan date. Enter missing ingredient prices yourself. A blank row must not make crafting look cheaper. Resale also has actual auction costs, and an asking price does not guarantee a buyer.
Work through five potions from beginning to end
Take Superior Mana Potion and use deliberately chosen practice prices: Sungrass 20 silver, Blindweed 30 silver and Crystal Vial 5 silver each. These are arithmetic examples, not current market or vendor prices. One potion costs 2 × 20 + 2 × 30 + 5 = 105 silver, or 1 gold 5 silver. Five crafts need ten Sungrass, ten Blindweed and five vials, worth 5 gold 25 silver in total.
If you already own four Sungrass and two Blindweed, you still need six Sungrass, eight Blindweed and five vials for the five potions. At the same example prices, the additional purchase costs 3 gold 85 silver. The value of all ingredients consumed remains 5 gold 25 silver. That is why a shopping list and a profitability comparison should not necessarily show the same number.
Now compare the price of five finished potions, not just one, against your full costs. For personal use, time and already knowing the recipe also matter. For a sale, include the actual auction costs as well. If an imported price is missing or an offer applies to a different stack size, fix that before deciding how many to make.
Calculate a small batch first
Compare one craft, then your desired quantity. If buying is cheaper, keep or sell the ingredients separately. If crafting wins, check the recipe, skill and required workstation before buying in bulk.