Figuring out the amount of down you need for your underquilt is fairly easy thanks to Hammock Forums user CatSplat, who created the Differential Cut UQ Calculator. This is a fast and easy way to calculate your down requirements and get estimates on the final weight and temp ratings.*
You can access the file via Google Drive HERE**, or download the Excel version attached to this article.
Please see below for a basic walkthrough of how to use this document.
To calculate your down requirements, fill out the following information:
Enter your desired finished Length and Width. (1)
Enter your desired baffle height (the baffle wall height), and the maximum baffle height. (2)
Choose the number of baffles you want. (3)
Enter the fill power of the down you want to use, and the amount of overstuff you want. (4)
Enter in the weight of the shell materials you're using. (5)
The calculator will then give you the following information:
The length and width of both the inner and outer layers, along with the width of each baffle. (6)
The amount of down you need to stuff in each chamber. (7)
The total amount of down you need for the entire project. (8)
The approximate weight* of the quilt, not including suspension (excluding channels, hardware, and suspension) (9)
The approximate temp rating of the finished quilt* (10) (This information is located on the right side of the spreadsheet)
* While we have built several quilts using this calculator, and they have been true to weight and temp, we cannot guarantee the results.
** In order to edit the file on Google Drive, you will need to make a copy by clicking on File->Make A Copy
*** Overstuffing a quilt will give you warmer results. It provides a denser insulation, helping the down hold onto warm air better. After 20-25%, the effectiveness of overstuffing will start to suffer from diminishing returns, where the mass of down will not allow for enough air to be trapped, causing a loss of efficiency.