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Unit Price Calculator

The ultimate shopping companion. Compare unlimited items across different units (oz vs g, L vs gal), calculate specific gravity conversions, and visualize annual savings immediately.

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About

Retail packaging is designed to confuse. Is the Family Size box of cereal actually cheaper per gram than the standard box? Does the 2-liter bottle of olive oil offer better value than the 3-gallon tin imported from Italy? The Unit Price Calculator eliminates this ambiguity by normalizing every product to a common baseline.

Unlike basic calculators, this tool features a Cross-Dimensional Engine. It seamlessly compares Mass (weight) against Volume (liquid) by applying density factors for common household substances like Milk, Flour, or Detergent. It handles imperial and metric units simultaneously, ensuring you never overpay due to confusing labels. Precision is key: we track costs down to the micro-cent.

shopping grocery budget bargain comparison

Formulas

The core mechanism normalizes all inputs to a standard base unit (g or ml) before comparison. The standardized price Pstd is calculated as:

{
PriceQty × kunit if same dimensionPriceQty × kunit × ρ if Mass ↔ Vol

Where kunit is the conversion coefficient to grams/milliliters, and ρ (rho) is the density of the substance (e.g., for Olive Oil ρ ≈ 0.92 g/ml).

To determine the savings S over a year (t = 52 weeks), we compare the selected item against the most expensive option:

Syear = itemsΔ (Pworst − Pbest) × Consumption

Reference Data

UnitTypeBase Conversion (g/ml)Notes
kgMass1000Kilogram (SI Base)
lbMass453.592Avoirdupois Pound
ozMass28.3495Avoirdupois Ounce
stMass6350.29Stone (UK)
gal (US)Volume3785.41US Liquid Gallon
fl oz (US)Volume29.5735US Fluid Ounce
cupVolume236.588US Legal Cup
tbspVolume14.7868Tablespoon
pt (UK)Volume568.261Imperial Pint

Frequently Asked Questions

Use the "Substance Mode" selector at the top of the calculator. By selecting a specific substance (e.g., "Cooking Oil" or 'Flour'), the calculator automatically applies the correct density (Specific Gravity) to convert volume to weight, allowing accurate cross-dimensional comparison.
Yes. The unit database distinguishes between US Fluid Ounces (29.57ml) and UK Imperial Fluid Ounces (28.41ml), as well as Gallons, Pints, and Quarts. Select the specific flag-marked unit from the dropdown.
The "Best Deal" is determined strictly by the lowest price per standardized base unit (e.g., Price per 100g or Price per 100ml). The tool highlights the mathematical winner, but you should also consider perishability and storage space.
Small differences compound over time. A saving of $0.05 per ounce on coffee can amount to over $100 a year for a heavy drinker. The calculator assumes a standard weekly consumption rate to project these long-term benefits.