Enter the total price and the quantity (ounces, pounds, liters, sheets, anything) for each product. Use the same unit for both.
The unit price is the price divided by the quantity. The product with the lower unit price costs less for the same amount, so it is the better deal on price alone. Make sure both quantities use the same unit, for example both in ounces, before comparing.
No. Bulk sizes are often cheaper per unit, but not always, so it is worth checking with a calculator.
Convert one of them first, for example 1 pound is 16 ounces and 1 liter is about 33.8 fluid ounces.
See also: Discount Calculator · Sales Tax Calculator · Percent Change Calculator