Postage and packing is calculated by weight, and goes up in weight bands (100 grams / 250 grams etc. as we would pay at the post office.) 
You can easily see how much an order would cost to post at any point - to see how it works simply follow these steps -

Put any item into your shopping basket.
Then click on "View Shopping Basket" (to the right of the search box)
This will take you to the Shopping Basket page.

At the centre of the page scroll down to your country and then click on the "Get Postage" button.
You will be able to see the cost of the postage for the regular postal service or the cost if sent by registered post.

The Table below illustrates the charges for standard post:           NB. the vast majority of orders are less than 250 grams.

We are sorry but we are unable to deliver to the USA at the moment. We don't have the facilities for the extra administration during busy periods to comply with the new regulations for sending post to the USA.

Spain: We can only deliver to mainland addresses. There is no reliable shipping available to us to deliver to the islands.

* There are some countries that we can only send to using Registered Post.

The table is for illustrative purposes only and should not be considered as a quotation.

It would be far simpler for us to charge a standard rate irrespective of size.  However, here at Seedaholic we do not believe that customers should ever be in a position that they are subsidising other people's orders, or that the cost of the seed packets for everyone are increased in order to cover possible delivery expenses.