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Unit Price Calculator

The big bag is not always the best deal. Compare up to three package sizes by price per ounce, pound, gram, or count — mixed units welcome — and run the shrinkflation check when a pack quietly gets smaller.

Which size is actually the cheapest?

Enter each package's price, size, and unit — ounces and grams can mix freely. The ranking updates as you type. Flip to the second tab to check whether a "new look" package is quietly charging you more per unit.

How it works: each item's size is converted to the display unit (1 lb = 16 oz, 1 kg = 1,000 g, 1 gal = 128 fl oz), then unit price = price ÷ converted size. Items must all be the same kind — weight, volume, or count — because price per ounce and price per fluid ounce answer different questions.

How it works: both packs are reduced to price per unit, then compared: unit-price change = (new − old) ÷ old. A smaller pack at the same price is a hidden price increase — the classic example above is a 2 oz disappearance that quietly raises the real price by 20%.

How unit price math works

Unit price is the great equalizer of the grocery aisle: it strips away the packaging, the "family size" branding, and the sale stickers, and reduces every option to one comparable number — what each ounce, gram, or item actually costs. Two packs can look wildly different on the shelf and cost exactly the same per unit; two "great deals" can differ by 20% once the math is done.

The formulas

unit price = price ÷ size (in one consistent unit) · comparing grams with ounces: convert first — 1 oz = 28.35 g · shrinkflation: unit-price change = (new unit price − old unit price) ÷ old unit price

The only rule that matters: compare like with like. Ounces and fluid ounces are not the same (one is weight, one is volume), grams and milliliters are not the same, and "each" only works when the items are truly identical. This calculator refuses mixed kinds for exactly that reason — an honest error beats a confident wrong answer.

Worked example: three boxes of cereal

The shelf: Cereal A, 12 oz for $4.99; Cereal B, 20 oz for $7.99; Cereal C, 32 oz for $11.49. Dividing each price by its size: A = $4.99 ÷ 12 = $0.416/oz, B = $7.99 ÷ 20 = $0.400/oz, C = $11.49 ÷ 32 = $0.359/oz.

The verdict: Cereal C wins — $0.06 cheaper per ounce than the priciest box. The middle box looks like the "sensible compromise" but it is barely cheaper per ounce than the small one. Over a year of weekly boxes, the bulk choice saves real money; over a year of middle-box "compromises," it quietly doesn't.

The middle-size trap

Retailers know shoppers assume "bigger is cheaper per unit" — so the middle size often carries the highest margin per unit of the three. The small size is priced to look affordable, the big size to look like a deal, and the middle one coasts on the assumption. Sale prices and coupons flip the math too: a 20%-off small pack routinely beats the full-price bulk pack. Always rerun the numbers on sale — never assume the bulk pack stays the winner.

Where this comes in handy

Weekly grocery runs: the unit-price guide teaches the full shelf-reading method — tags, traps, and the waste rule.
Recipe ingredients: buying flour, sugar, or oil in bulk? The cooking converter turns cups into grams so you know how much the recipe actually needs.
Sale stacking: a 25%-off sticker changes everything — run the discounted price through the discount calculator first, then compare per unit.
Eating out vs. cooking: the tip calculator settles the restaurant bill — then unit pricing settles whether cooking that meal at home was the real deal.
Percentage savings: want the saving as a percent instead of dollars per ounce? The percentage calculator converts it.

Unit price — frequently asked questions

How do I calculate unit price by hand?

Divide the price by the size: $4.99 ÷ 12 oz = about $0.42 per ounce. That's it — one division. The only hard part is keeping the units consistent, which is why comparing a 500 g bag with a 1 lb bag needs a conversion first (1 lb = 453.6 g).

Should I compare per ounce or per pound?

Either works, as long as every option uses the same one. The trap is mixing them: "$0.42/oz" looks cheaper than "$5.99/lb" until you realize $0.42/oz is $6.72/lb. Pick one unit and convert everything to it before deciding.

Is the biggest package always the cheapest per unit?

Usually, but not reliably. The middle size often has the highest per-unit margin — priced to look like a compromise while quietly costing more than the small one per ounce. Sales, coupons, and club-pack pricing flip the ranking constantly, so the "bulk is best" rule needs a calculator, not faith.

How do I compare grams with ounces, or ml with cups?

Convert one side: 1 oz = 28.35 g, 1 cup = 236.6 ml. The calculator above does this automatically — pick different units per item and it converts everything to your chosen display unit before ranking.

How do I spot shrinkflation?

Check the net weight on the new package against what you remember (or an old photo). Same price + smaller size = higher unit price, always. The shrinkflation tab above does the math: if the pack shrank and the unit price rose, it names it plainly.

Can I trust the unit price on the shelf tag?

Mostly — many states require it — but read the unit. Tags sometimes switch between per-oz, per-lb, and per-100-count to make comparisons awkward, and rounded tags can hide a few cents. When two tags use different units, do the division yourself.

Should I always buy the cheapest per unit?

Only if you'll actually use it. The waste rule beats the unit-price rule: a bulk pack that goes stale, expires, or gets thrown away is infinitely expensive per unit consumed. Buy the cheapest per unit among sizes you will finish — that's the real win.

Learn the method: the free unit-price guide walks through reading shelf tags, the middle-size trap, shrinkflation math, and when bulk buying loses money — step by step with worked numbers.