There are many ways to ship an item with Open Cart. This is an explanation of weight based. Just which one your company decides to use will be a personal choice that has a lot to do with what you are selling and what your budget currently is.
Question: How does weight-based shipping work?
Weight based shipping uses your own personal “table” rates to determine the shipping cost.
It allows multiple ranges of rates based on different weights. The format of the weight to cost in the admin area is:
weight:cost, weight:cost, etc
For example if you want to setup the following:
Cart weight 10lbs or less cost $10
Cart weight 11-20lbs cost $15
Cart weight 21-40lbs cost $20
Cart weight more than 40lbs cost $30
You would use the following rates:
10:10.00, 20:15.00, 40:20.00, 9999999:30.00
The last one is important because it sets a virtually infinite ceiling. If you didn’t have that 9999999 rate, then anything over 40lbs would have no available rate and would not show.
Weight-Based shipping also supports multiple geozones. Read http://forum.opencart.com/viewtopic.php?f=20&t=7099 here for understanding geozones. Each geozone can have its own set of weight:cost ranges.