Packing the car seat is a lot more easier if you still have its original box. Just place the boxed seat into a larger shipping box and fill the spaces with packing materials to prevent movement during transit.
However, if the original box is not available anymore, you can buy sturdy boxes from shipping supply stores. Take the car seat’s measurements so that you can get a box as close to the size of the seat as possible. You do not want a box that is too big, as it can result in postage for a over sized package.
Wrap the car seat with bubble wrap and place it inside the box. Fill the remaining spaces with more bubble wrap, packing peanuts or bagged air to cushion it against damage while in transit. Make sure to package it well as a damaged car seat is not safe for the child and cannot be used.
Seal up with the car seat box with some strong packing tape.
Measure the length, width and height of the package. Packages mailed through the U.S. Postal Service that exceed 108 inches total for priority mail or 130 inches for parcel post are subject to an oversize package fee. Write down your measurements. Use a scale to weigh the package. You can use a regular bathroom scale.
Input your package dimensions and weight on the USPS online shipping calculator to get a shipping quote. Do the same on the UPS and FedEx websites. This will give you an idea of where you will get the best price on shipping the car seat.
Take your package to the place that had the best shipping quote. Present your package to the clerk for shipping and pay the shipping fee.