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BuyPerUnit

How BuyPerUnit Works: Our Price-Per-Unit Methodology

BuyPerUnit calculates cost per unit for every product by dividing the current retail price by the product's capacity or yield. For storage, this means $/GB (price ÷ gigabytes). For printer ink, this means $/page (price ÷ estimated page yield). Prices are sourced daily from Amazon, Best Buy, and Newegg via their product APIs.

How We Calculate $/GB for Storage

We divide the current retail price by the stated storage capacity in gigabytes. For terabyte drives, we multiply the TB count by 1,000 (e.g., 2TB = 2,000GB).

$99.99 price ÷ 2,000 GB capacity = $0.0499/GB

How We Calculate $/Page for Printer Ink

Printer ink and toner are calculated using the manufacturer's stated "page yield" — the estimated number of pages a cartridge can print based on standard ISO coverage tests. We divide the retail price by this yield to get the true cost per page.

$45.00 price ÷ 1,500 page yield = $0.030/page

Where Our Price Data Comes From

We do not scrape HTML. We pull structured data directly from official retailer APIs to ensure accuracy:

  • Amazon: Amazon Creators API
  • Best Buy: Best Buy Products API
  • Newegg: Rakuten / Newegg Partner Feed

How Often Prices Update

Our backend syncs prices automatically twice daily — at 6:00 AM and 6:00 PM UTC. When a product drops out of stock at a retailer, it is automatically removed from our database during the next sync to ensure you only see purchasable items.

How We Handle Refurbished Products

We include refurbished, renewed, and renewed-premium products in our database because they often provide the absolute lowest $/GB available. However, these are always explicitly tagged with a Refurbished badge so you can easily distinguish them from new hardware.

How We Handle Shipping and Tax

Our price-per-unit calculations are based purely on the base retail price of the item. Because shipping costs and sales tax vary wildly based on your location and membership status (like Amazon Prime or Best Buy Total), we do not factor these variables into the $/GB calculation.

Our Accuracy and Limitations

BuyPerUnit is a math-first engine. We sort strictly by price per unit. We do not test read/write speeds, IOPS, or hardware reliability. If pure performance matters more to you than price, we highly recommend checking benchmarks on specialized hardware review sites. We are the tool you use to verify you aren't overpaying once you know what class of product you need.

Frequently Asked Questions

Do commissions influence your rankings?▾
Never. Products are always ranked strictly by lowest price per unit. While we earn affiliate commissions when you purchase through our links, this financial relationship has zero impact on the sorting order.
Why do you only track Amazon, Best Buy, and Newegg?▾
We focus on these three retailers because they represent the vast majority of consumer tech purchases, offer reliable APIs for daily price syncing, and maintain strict policies against counterfeit storage products.
What if a listed price is wrong?▾
Because prices change constantly, a retailer may occasionally adjust a price between our daily syncs. The price shown on the retailer's actual website at checkout is always the final, correct price.
Why don't you include performance benchmarks?▾
BuyPerUnit is built entirely around price efficiency. While speed is important, adding performance metrics would dilute our core mission: finding the cheapest possible unit of storage or ink. For performance reviews, we recommend sites like Tom's Hardware.