I've no objection to Theo's suggestion as long as you don't mind overfeeding your trout. Trout will consume more formulated feed than they should in a feeding. IOWs, more than they can efficiently metabolize before passing the meal. Understanding the proportion of feed as it relates to the weight of the fish can help you more efficiently utilize the feed, if that is important to you. You are feeding in a pond (hopefully at low density) and so long as the pond can supply additional nutrition in the form of invertebrates and minnows you don't have to feed all of the nutritional needs in the form of feed for maximum growth. For example, if you feed at 80%, they would make up the remainder of the 20% needed for maximum growth from pond organisms. The calculated efficiency of the feed would improve by 20%.

You don't have to weigh fish. Just be able to sample average lengths while fishing to understand average weights. Feed them according to standard weights for length. That's how the spreadsheet works above.

But again, the world will not end if you waste some feed. It's OK to do that.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers