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Unit Price Comparison Calculator

Divides each price by its quantity to get the price per unit, tells which of two options is cheaper per unit and by what percentage.

When to use

You are comparing two package sizes or brands of the same product (e.g. 500 g for 3.49 vs 1 kg for 5.99) and want the better value per unit.

Do not use when: The two quantities are in different units (convert them to the same unit first, e.g. with mass or volume), or you need a discount on a single price (use discount).

Formula

unit_price = price / quantity; savings_percent = (max(unit_price_a, unit_price_b) − min(unit_price_a, unit_price_b)) / max(unit_price_a, unit_price_b) × 100

Inputs

Parameter	Type	Required	Description
`price_a`	number	yes	Total price of option A. Range: ≥ 0, ≤ 100000000
`quantity_a`	number	yes	Quantity in option A (grams, kilograms, litres, pieces …). Range: > 0, ≤ 1000000000
`price_b`	number	yes	Total price of option B. Range: ≥ 0, ≤ 100000000
`quantity_b`	number	yes	Quantity in option B, in the same unit as quantity_a. Range: > 0, ≤ 1000000000

Outputs

Output	Type	Unit	Description
`unit_price_a`	number		price_a / quantity_a, per one unit of quantity.
`unit_price_b`	number		price_b / quantity_b.
`cheaper_option`	string		'Option A', 'Option B' or 'Same unit price'.
`savings_percent`	number	%	How much lower the cheaper unit price is, relative to the more expensive one.
`unit_price_difference`	number		\|unit_price_a − unit_price_b\|.

Example

0.5 kg for 3.49 vs 1 kg for 5.99: {"price_a":3.49,"quantity_a":0.5,"price_b":5.99,"quantity_b":1} → {"unit_price_a":6.98,"unit_price_b":5.99,"cheaper_option":"Option B","savings_percent":14.18,"unit_price_difference":0.99}

12 eggs for 2.00 vs 18 eggs for 3.30: {"price_a":2,"quantity_a":12,"price_b":3.3,"quantity_b":18} → {"unit_price_a":0.1667,"unit_price_b":0.1833,"cheaper_option":"Option A","savings_percent":9.09,"unit_price_difference":0.0167}

GET https://tttkmbb.com/api/v1/calculate/unit-price?price_a=3.49&quantity_a=0.5&price_b=5.99&quantity_b=1

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/unit-price (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/unit-price · Markdown: https://tttkmbb.com/everyday/unit-price.md · JSON definition: https://tttkmbb.com/everyday/unit-price.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="unit-price"
OpenAPI operationId: calculate_unit_price
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Unit price (Wikipedia) (reference)
EU Directive 98/6/EC on the indication of unit prices (standard)

FAQ

Which unit should I use for the quantities?

Any unit, as long as both options use the same one; unit prices are then per that unit. Using kg or L instead of g or ml gives more readable unit prices.

Is the larger package always cheaper per unit?

No. Promotions on small sizes frequently undercut bulk packs, which is exactly what this comparison reveals.

Related calculators

Discount Calculator — Apply a percentage discount to a price.
Percentage Change Calculator — Percentage difference between two prices.