Put the formulas to work

Worked shopping examples

Each example starts with the package labels and ends with the decision information those numbers support. Prices are invented for explanation; replace them with the offers in front of you.

Different package sizes: 12 oz versus 18 oz

A 12 oz bag costs $3.49 and an 18 oz bag costs $4.79. Divide price by ounces: $3.49 ÷ 12 is about $0.291 per ounce; $4.79 ÷ 18 is about $0.266. The 18 oz bag is lower by roughly 2.5 cents per ounce.

At 18 ounces, the smaller bag’s rate would cost about $5.24, so the larger bag is roughly 45 cents cheaper for an equal amount. It still costs $1.30 more at checkout than one small bag. Compare these deals when the shelf prices change.

Multipacks with different contents

Deal A is four 12 oz bottles for $10.80: 4 × 12 = 48 fl oz, or $0.225 per fl oz. Deal B is six 8 oz bottles for $11.52: also 48 fl oz, or $0.24 per fl oz. Comparing only four bottles with six would incorrectly favor the package with more containers. Here the total volume is equal and Deal A saves 72 cents.

Mixed units: 16 oz versus 1.5 lb

A 16 oz package is $4.64. A 1.5 lb package is $6.48. Convert 1.5 lb × 16 = 24 oz. The first costs $0.29 per ounce; the second costs $0.27 per ounce. The 1.5 lb package has the lower unit price, although it needs $1.84 more at checkout.

A sale sticker versus a larger regular package

A sale bag contains 10 oz for $3.20. A regular 24 oz bag costs $7.20. The sale bag is $0.32 per ounce; the regular larger bag is $0.30. The sale is real relative to its former price, but it is not the lowest unit-price option in this comparison.

Percentage off versus dollars off

On a $30 item, 20% off saves $6 and produces a $24 final price. A $5 coupon produces $25, so percentage off wins by $1. On a $20 item, 20% saves $4 and the $5 coupon wins by $1. The coupon headline cannot be compared without the eligible price. Try the Coupon & Discount Comparator with sale prices and quantities.

An incomplete BOGO group changes the price

Suppose an item costs $8 with Buy 2 Get 1 Free. Three items form one complete group, so you pay $16 and the effective price is about $5.33 each. Six items form two groups, cost $32, and keep the same effective price.

If you need five items, only one complete group qualifies. The remaining two cost full price, producing a $32 checkout total and a $6.40 effective price. The Buy X Get Y Calculator applies that remainder automatically and can compare it with a straightforward sale.

Use the right tool for the question

Compare Deals answers which package has the lower normalized price. The BOGO calculator applies complete Buy X Get Y groups, while the coupon tool handles sale prices plus percentage or dollar-off coupons. The Usage Tracker records household consumption separately. The methodology documents the exact rules behind all four.