Compare unit price between products
A 12-item pack at 4.50 costs 0.375 per item, while a 20-item pack at 6.40 costs 0.32, so the bigger pack is the better value. Enter the price and size of two products and see both unit prices and which one wins. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Product a price
- 4.5
- Product a size
- 12
- Product b price
- 6.4
- Product b size
- 20
- Better value
- product_b
- Difference per unit
- 0.055
This unit price comparison calculator turns two package prices and sizes into a fair, like-for-like cost comparison. Enter the total price and package size for product A and product B, using the same unit for both sizes. The calculator divides each price by its size, reports both prices per unit, and identifies the lower-cost choice or a tie. It is useful for groceries, household supplies, office purchasing, and any decision where packages contain different quantities. A zero or negative package size is rejected because it cannot produce a meaningful unit price.
Why unit price gives a fair comparison
Shelf prices alone do not tell you which package offers better value when the quantities differ. A smaller box may look cheaper at the register while costing considerably more for every ounce, gram, milliliter, sheet, capsule, or item it contains. Unit price solves that problem by placing both products on the same basis.
The calculation is simply package price divided by package size. For example, a twelve-item pack priced at 4.50 has a unit price of 0.375 per item, while a twenty-item pack priced at 6.40 has a unit price of 0.32 per item. Although the second package costs more in total, it provides the lower cost per item and is therefore the better value under this comparison.
The result focuses only on quantity economics. It does not decide whether you need the larger package, whether it will expire, or whether quality differs. Those practical factors still matter, but unit price gives you the clean numerical fact needed to evaluate the price side of the decision without being distracted by package shape, promotional wording, or the larger number printed on one label.
How to enter prices and package sizes correctly
Enter each product's complete package price as a plain number and its complete package size as another number. Both sizes must use the same unit. You can compare two cereal boxes measured in ounces, two detergent bottles measured in milliliters, or two multipacks measured by item count.
Do not compare ounces directly with grams or liters directly with milliliters; convert one size first so the denominators match. Prices may be zero, which can represent a genuinely free sample, but they cannot be negative. Package sizes must be greater than zero.
A zero size would require division by zero, and a negative size does not describe a real quantity, so either condition returns an invalid-input error instead of a deceptive answer. The result contains a record for product A and product B, preserving each entered price and size and adding the calculated unit price.
Interpreting the better value result in practice
The product marked as the better value has the lower calculated price for one shared unit. That is a precise mathematical result, but buying decisions often include constraints beyond arithmetic. A bulk package can have the best unit price and still waste money if part of it spoils, occupies unavailable storage, or exceeds your immediate budget.
A smaller package can be rational when you are testing a product, traveling, or avoiding waste. Taxes, coupons, membership fees, delivery charges, loyalty discounts, deposits, and differences in quality are not added automatically; use the final price you expect to pay if those adjustments belong in your comparison. The difference per unit helps judge significance.
A tiny difference may not outweigh convenience or preference, whereas a large difference repeated across hundreds of units can materially affect a household or procurement budget. The calculation is deterministic and uses no network, current price feed, random value, or clock. Identical numeric inputs therefore produce identical results.
For auditable purchasing, record the source prices, ensure the size units match, and retain the returned unit prices alongside the final decision.
What you can do with it
Compare grocery package sizes
Check whether a larger jar, box, or multipack really costs less per ounce, gram, or item.
Evaluate household supply offers
Compare detergent, paper goods, batteries, and refills when package quantities and shelf prices differ.
Support purchasing decisions
Put two supplier packages on a common per-unit basis before choosing a line item for an order.
FAQ
How is the unit price calculated?
Each package price is divided by its package size. The product with the lower result is identified as the better value.
Do both package sizes need the same unit?
Yes. Convert the sizes to one common unit before comparing, such as both in grams, ounces, milliliters, or items.
Can a price be zero in the comparison?
Yes. A price of zero is allowed, for example for a sample handed out at no cost, but it cannot be negative. Package sizes, on the other hand, must be greater than zero, since a size of zero would mean dividing by zero.
What does the difference per unit tell me?
It is the gap between the two unit prices, 0.055 per item in the example. Multiply it by the quantity you expect to buy or use to see how much the choice is really worth to you.
Does the lower unit price always mean the better buy?
Only on price. The comparison does not know whether you need the larger pack, whether it will expire before you finish it, or whether the quality differs. Weigh those yourself once the numbers are clear.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/math/unit-price-compare \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"product_a_price":4.5,"product_a_size":12,"product_b_price":6.4,"product_b_size":20}'const res = await fetch("https://api.kit.forhosting.com/math/unit-price-compare", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"product_a_price": 4.5,
"product_a_size": 12,
"product_b_price": 6.4,
"product_b_size": 20
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/math/unit-price-compare",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"product_a_price": 4.5,
"product_a_size": 12,
"product_b_price": 6.4,
"product_b_size": 20
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/math/unit-price-compare", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"product_a_price":4.5,"product_a_size":12,"product_b_price":6.4,"product_b_size":20}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"product_a_price":4.5,"product_a_size":12,"product_b_price":6.4,"product_b_size":20}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/math/unit-price-compare", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"product_a_price": 4.5,
"product_a_size": 12,
"product_b_price": 6.4,
"product_b_size": 20
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "math.unit_price_compare",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
How to enter prices and package sizes correctly
The better_value field names product_a or product_b when one unit price is lower and reports tie when both rounded unit prices are equal. The difference_per_unit field shows the absolute gap, making it easier to estimate how much the choice matters across the quantity you expect to buy or use.
Interpreting the better value result in practice
API requests cost $0.002, while the browser experience can perform the same arithmetic locally.
Technical questions
What happens when a package size is zero or negative?
The request returns invalid_input because a package size must be positive to define a meaningful price per unit.
What happens if both products have the same unit price?
The better_value field reports tie, and the difference per unit is zero.
What does the comparison cost?
The browser calculation is free. A successful API request costs $0.002.