This link is the main menu for calculating shipping. Look on the left hand side of the page in the blue area for Domestic and International shipping. There is also a link in the body of the page.
USPS Calculate shipping
To calculate insurance you have to go through the process of calculating shipping. Only some of the international shipping options allow you to add insurance.
For Example a 1 lb package to the UK
You cannot get insurance on Global Priority, Air Mail Letter Post, or Ecomony Surface Letter Post.
You can get insurance on Airmail Parcel Post, Surface Parcel Post but you will notice that it is an extra charge and those shipping options are much more expensive.
On Global Express (EMS not guaranteed Express) insurance for up to $100 is incuded. You have to pay for more than that at standard PO rates (same as domestic insurance).
I find that most times it is less expensive for the bidder if they ship Global Express if they want insurance. Compare surface parcel post with Express.......most times Express is only a few dollars more (and sometimes less--see below) and they get it in less than a week rather than 4-6 weeks.
For a 1 lb package to the UK
$24.75 for Global Express (EMS) with $100 insurance arrives in 3-5 days
$25.60 for Ecomony Surface Parcel Post $100 insurance arrives in 4-6 weeks
I only ship Global Express (insurance) or Global Priority (no insurance) now. I no longer ship air mail or surface mail due to too many lost and/or damaged packages. I was told by the Postmaster at the branch that I ship from, that the GP packages go in the same bag as Global Express mail. I pack very carefully and have not had a missing or damaged package in 2 years. I still give my international bidders the option to purchase insurance and state that I am not responsible if the item does not arrive, but also tell them that I have never had a damaged or lost package yet. They can make the decision on whether of not to spend the money for Express. It can get to be expensive.
I also use the Global Priority flat rate envelopes (insurance not available) for smaller items or books. They are the same size as the domestic priority envelopes and cost $5.00 (6 x 10--$4.00 to Canada) and $9.00 (9½ x 12½ --$8.00 to Canada). Saves the bidder lots of money.