Put both prices on the same scale
For products used in the same amount, divide each price by its volume. Here is a hypothetical comparison: a 500ml bottle costs £2.40 and a 1-litre refill costs £4.20. The bottle is 48p per 100ml; the refill is 42p per 100ml. Buying the refill saves 60p against buying two bottles at those example prices.
That saving changes if only one option qualifies for a voucher or the refill needs a separate delivery. Write down the price you would actually pay for each option, with any unavoidable order costs. A lower shelf price per millilitre is useful information, but it is not necessarily a lower cost for today's order.
Check what the refill is meant to refill
A similar scent or bottle shape does not establish compatibility. Look for the product name, formula and manufacturer's refill instructions. A concentrate requiring dilution should be compared using its stated prepared yield or recommended dose, not as if each millilitre were ready to use.
Do not mix different cleaning products or top up an unlabelled container. Follow the product instructions about emptying, cleaning and reusing its bottle. Keep the original product identification and handling information available. If the intended dispenser is damaged or cannot be safely reused, include a replacement in the comparison.
Allow for how you will store and pour it
The largest pouch is not automatically the easiest purchase to manage. Check its closure, the weight you will lift and the space needed to keep it upright. A small price advantage can disappear if a hard-to-control pour wastes part of the product. Choose a refill size that suits the container and the person doing the refilling.
Estimate how long the remaining quantity will last from your usual use, rather than an optimistic plan to clean more often. Keep products under the storage conditions shown on the label and away from children or pets as directed. Buying several pouches at once only helps if you can store and use them appropriately.
Keep cost and packaging claims separate
A pouch may use less packaging material than several rigid bottles, but that does not tell you how it can be recycled locally. Check the pack's material information and your collection options instead of assuming that ‘refill’ means every part belongs in a household recycling bin.
For a repeat purchase, keep a short note of the product, normal bottle price, refill price and usable quantity. That gives the next promotion something concrete to beat. You can prefer the refill format and still choose a bottle on an occasion when the price, compatibility or storage works better.
