The bigger packet isn’t always the better bargain. And a bright yellow sale sticker doesn’t tell you what something costs per 100 grams. If supermarket maths makes your eyes glaze over, ChatGPT can help you compare the numbers you see on the shelf.
What you’ll learn: how to compare two grocery products using their unit prices, without asking AI to invent today’s specials.
What is a unit price?
A unit price tells you what an item costs for a standard amount, such as 100 g, 1 kg, 100 mL, 1 L or one item. Comparing the same unit makes different pack sizes easier to judge. Australian supermarket shelf labels commonly show unit pricing, but always check the actual label for the product you’re buying.
Try it in five easy steps
- Choose two similar products you would genuinely use, such as two bags of rice or two tins of tomatoes.
- Write down each shelf price and pack size. You can use the unit price already printed on the shelf label if it’s clear.
- Paste the prompt below into ChatGPT, then enter your product details. You don’t need to upload a receipt or a photograph.
- Check the arithmetic with a calculator or the shelf labels. Compare the same units and watch for multi-buy conditions.
- Choose based on value and what suits your household. A larger packet isn’t a saving if half goes to waste.
Copy-and-paste ChatGPT prompt
Tap and hold the text below to copy it, then paste it into ChatGPT.
I’m shopping in Australia and want to compare grocery value without guessing prices. Help me compare items using the price and pack size I provide. Ask me to list each item like this: item name, shelf price in Australian dollars, pack size in grams, kilograms, millilitres, litres or number of items. Calculate the unit price per 100 g, per kg, per 100 mL, per litre or per item, using the same unit for products being compared. Show the calculation in simple steps. If a detail is missing, ask rather than invent it. Remind me to check whether the products are genuinely comparable in quality, ingredients and what I will actually use. Keep the answer short and easy to read.
A simple example: two bags of rice
These are made-up example prices, not current supermarket offers.
Bag A: 500 g for $2.40. That’s $4.80 per kg (because 500 g is half a kilogram).
Bag B: 1 kg for $4.20. That’s $4.20 per kg.
Bag B costs 60 cents less per kilogram. But Bag A might still be the sensible choice if you only need a small amount, have limited storage or won’t finish a larger bag before it deteriorates.
Three things AI cannot safely assume
- Current prices: ChatGPT may not know what your local supermarket is charging today. Enter prices from the actual shelf or a current retailer listing.
- Identical products: A lower unit price does not automatically mean equivalent quality, ingredients or dietary suitability.
- Special conditions: Check loyalty prices, multi-buy offers, expiry dates and limits yourself before paying.
Keep your shopping details private
You only need product names, pack sizes and prices. Don’t upload loyalty card numbers, payment details, addresses or full receipts with identifying information. If you use a photo, crop out personal details first.
One small challenge for your next shop
Pick just one everyday item, such as oats, pasta or laundry detergent. Compare two sizes using the shelf labels, then ask ChatGPT to explain the calculation. Once you’ve tried it, you’ll know how to do the same comparison again.
Want more easy ways to use AI? Browse our Free AI Resources library for beginner-friendly prompts you can copy and try.
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