One honey is sold by grams and another by millilitres: why won't the tool compare them?
Because grams measure mass and millilitres measure volume, and you cannot convert between them without the product's density, which differs for honey, oil or shampoo. Rather than give you a number built on a guess, the tool stops and explains why. The fix is to find the other unit on the pack, or compare packs labelled in the same kind of unit.
What you see exactly
I entered one honey at 45 for a 500 g jar and another at 38 for a 350 ml jar. The tool showed no table, but a message saying the options cannot be compared because their units are different kinds of measure, listing each option with its kind: the first mass, the second volume. It asks you to pick units of the same kind for every option.
Why it will not assume 1 ml equals 1 g
That shortcut only roughly holds for water. Honey is clearly heavier than water, so a 350 ml jar of honey weighs more than 350 g. If the tool assumed 1 ml = 1 g, it would understate the second jar's contents and make it look more expensive than it is. Oil goes the other way, being lighter than water. Any number it showed would be wrong for some product, so it shows none.
Three ways to compare properly
- Look for the net weight on the second jar. Many packs print both weight and volume, or the weight in small print on the back.
- If you find it, enter both options in grams in the Unit-price comparison tool, and the comparison appears at once.
- If the second jar only shows volume, ask the seller for the net weight, or compare it with other packs labelled in millilitres only.
Example: the back of the second jar says net weight 400 g. Entering 45 for 500 g and 38 for 400 g gives 90 per kg for the first and 95 per kg for the second, so the second is 5.56% more expensive. The cheaper jar on the shelf is not the cheaper one per kilo.
Similar cases you will run into
- Olive oil in ml against oil sold in grams: same rule, find the shared unit.
- A product by the piece against one by weight, such as eggs per piece and eggs per kilo: the tool refuses too, because turning a count into a weight needs the weight of one piece.
- Eastern Arabic digits on a pack, such as ٤٠٠, are accepted in the fields, and if you want to copy them into a spreadsheet, convert them with the Arabic/Persian/Western digit converter.
If one of the jars is on offer, work out the price after the discount first with the Discount calculator, then enter it in the comparison.
Common questions
Can I add the density by hand in the tool?
No, there is no density field. Compare using the units printed on the packs.
Is an ounce mass or volume?
In the tool, oz is mass and fl oz is volume, and they sit in different groups.
Will the tool refuse grams with kilograms?
No. Both are mass, so it converts and compares directly.