Calculateur de Prix Unitaire - Trouver le Meilleur Prix

How to Calculate Unit Price

Unit price is the cost per single unit of measurement, making it easy to compare different package sizes. The formula is simple: Unit Price = Total Price ÷ Quantity.

Example: A 32 oz bottle of shampoo for $3.99 vs. a 48 oz bottle for $5.49:

• 32 oz bottle: $3.99 ÷ 32 = $0.1247 per oz
• 48 oz bottle: $5.49 ÷ 48 = $0.1144 per oz
• The larger bottle is cheaper by $0.0103 per oz (8.3% savings)

Retailers are often required by law to display unit prices on shelf tags. When they don't, or when comparing across stores, this calculator does the work instantly.

When Bigger Isn't Always Better

The larger package often (but not always) has a lower unit price. Before assuming the biggest is cheapest, check these factors:

For non-perishable items you use regularly, buying in bulk at a lower unit price usually saves money. For specialty items you rarely use, the smaller package may save money overall by avoiding waste.

Unit Price Comparisons: Common Units

Different products use different quantity units. Convert to a common unit for fair comparison:

Unit Conversion Reference for Shopping

When comparing products with different measurement systems, use these exact conversions:

Tip: When a US product lists "per ounce" and a European product lists "per 100g," convert the US price to per-gram first (divide by 28.35), then multiply by 100 to get the comparable per-100g rate.

Real-World Unit Price Comparisons

These examples illustrate how unit price analysis works for common grocery categories. Prices are approximate US averages (2024):

Bulk savings of 25–40% are typical for shelf-stable products. However, the absolute savings depend on your consumption rate — if you throw out half the bulk product, you haven't saved anything.

Shrinkflation: Hidden Unit Price Increases

"Shrinkflation" occurs when manufacturers reduce product quantity while keeping the price the same (or even raising it slightly). The unit price increases, but the shelf price looks unchanged. Tracking unit price is the only reliable way to detect it.

Notable examples of shrinkflation (2020–2024):

The US Bureau of Labor Statistics (BLS) adjusts the Consumer Price Index (CPI) for package size changes, so shrinkflation does get captured in official inflation figures. But at the individual shopping level, only unit price comparison protects your budget.

Unit Price Laws and Regulations

Many jurisdictions require retailers to display unit pricing on shelf tags. The requirements vary:

Even where unit pricing is displayed, different stores sometimes use different units for the same product category (per oz vs. per 100g), making direct shelf-to-shelf comparison harder. This calculator normalizes everything to the same unit.

Advanced: True Cost per Use

For some products, "cost per unit of weight" isn't the best comparison. Cost per use accounts for concentration, dilution, or effectiveness differences:

To calculate cost per use: (Price ÷ Number of uses per package). For concentrated detergent: if a 100 oz bottle at $12.99 does 64 loads, the cost is $12.99 ÷ 64 = $0.203 per load. Compare that to a 150 oz regular bottle at $14.99 doing 52 loads: $14.99 ÷ 52 = $0.288 per load. The concentrated version wins despite having fewer ounces.

Grocery Budget Savings Strategy

Research published in the Journal of Consumer Research and by the USDA Economic Research Service consistently shows that unit-price-aware shoppers save 15–25% on groceries. Here is a practical strategy:

1. Always check unit price first — ignore the shelf price until you've compared unit costs
2. Buy store brands for staples — store brands are typically 20–30% cheaper per unit for identical ingredients (flour, sugar, salt, canned vegetables)
3. Buy bulk for non-perishables you use weekly — rice, pasta, cooking oil, cleaning products, paper goods
4. Buy small for perishables unless you'll consume everything — fresh produce, dairy, bread
5. Factor in coupons and sales — always recalculate unit price after discounts; a BOGO deal on a small package may beat the bulk unit price
6. Track prices over time — keep a short list of unit prices for your top 20 items to recognize real deals vs. fake "sales"

For a family spending $800/month on groceries, a 20% savings from consistent unit-price shopping is $160/month — $1,920 per year.

Online vs. In-Store Unit Price Comparison

Online grocery shopping introduces new variables for unit price comparison:

To fairly compare online vs. in-store: add all fees (delivery, tip, subscription) to the online order total, then calculate the overall unit price. For example, a $120 online order with $10 delivery and $5 tip costs $135 total — the effective markup is 12.5%. This erases most bulk-discount savings unless the order is large enough to spread the fixed costs.

International Unit Price Comparison

When traveling or shopping internationally, be aware that unit pricing conventions differ:

Quick conversions for cross-border comparison: $1/oz = $35.27/kg. If olive oil costs €8.50/L in Spain and $0.47/oz in the US, the US price = $0.47 × 33.814 oz/L = $15.89/L ≈ €14.60/L at current exchange rates — nearly double the Spanish price. Unit price comparison across countries must always account for exchange rates, and prices fluctuate significantly by region even within the same country.

Unit Price for Subscription Products

Subscription services (diapers, pet food, coffee, razors) often advertise savings vs. one-time purchase. Calculate the true unit price including any commitment:

Always calculate the per-unit cost including shipping and any cancellation fees. Some subscriptions offer a low introductory rate that increases after 2–3 shipments — recalculate after the promotional period ends.