How this instrument works
Spreads vary a lot in how much mass fits in a level teaspoon, because density differs by product — a teaspoon of dense peanut butter weighs more than a teaspoon of runny honey, which weighs more than a teaspoon of light, whipped butter. That density, multiplied by how many teaspoons you spread on each slice and how many slices you eat per day, determines how fast a jar actually empties, independent of the jar's total price or size.
This calculator uses typical grams-per-teaspoon figures for six common spreads and combines them with your own daily habits to estimate both how many days a jar lasts and what that habit costs you per day. The density figures are reasonable category averages — a specific brand's density can run a little higher or lower — so treat the day count as a close estimate rather than an exact countdown.
- Pick your spread from the list.
- Set how many teaspoons you spread per slice and how many slices you eat per day.
- Enter the jar or tub size in grams and what it cost you.
- Read off how many days the jar should last and your cost per day.
A 400g butter tub at 4 slices a day
Butter runs about 5 g per teaspoon. At 2 teaspoons on each of 4 slices a day, that's 5 x 2 x 4 = 40 g of butter used per day. A 400 g tub divided by that daily rate gives 400 / 40 = 10.0 days before the tub is empty.
If that tub cost $4.50, the daily cost works out to $4.50 x (40 / 400) = $0.45 per day — a small enough number on its own, but one that adds up to about $13.50 over a full 30-day month of the same habit.
Questions
Why do different spreads use different grams per teaspoon?
Density is the reason: a teaspoon is a fixed volume, but how much mass fills that volume depends on the spread's composition. Jam and honey, which are dense and mostly sugar and water, weigh more per teaspoon than whipped butter or a lighter chocolate-hazelnut spread that's been aerated. That's why this calculator uses a separate density figure for each spread rather than a single number for all of them.
Will my jar actually last exactly this many days?
Close to it, but not exactly — the density figures used here are typical category averages, and real-world spreading is rarely perfectly consistent from slice to slice. Some days you'll spread thicker, some jars get scraped more thoroughly near the end than others, and brand-to-brand density does vary a little. Treat the result as a reliable planning estimate for budgeting and shopping, not a guarantee to the day.
How can I use this to compare spreads by cost?
Run the same slices-per-day and teaspoons-per-slice numbers through each spread option with its actual jar price, and compare the resulting cost-per-day figures directly — that isolates the cost difference to the spread itself rather than your eating habits. It's a quick way to see, for example, whether a pricier jar that lasts noticeably longer per teaspoon actually beats a cheaper one that gets used up faster.
What if I use more than one spread on the same slice?
Run the calculator once per spread with your actual teaspoons of that spread per slice, then add the resulting costs together — the tool is built around a single spread at a time, since each has its own density and jar size. This keeps the math for each ingredient accurate rather than trying to average two different densities into one combined figure, which would blur the per-spread cost you're usually trying to see.