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How to weigh eggs and calculate weight loss

Weigh egg trayWeighing your eggs is the best way to make sure you've got the humidity inside your incubator right.  I figured some of you might find the idea daunting, so I'll take you through it step by step.

First, you want to find the weight of your eggs at the time you put them in the incubator.  There's no need to weigh one egg at a time --- just put all of the eggs on a scales at once.  If you're lucky and your tray of eggs can be lifted straight out of the incubator (like in our new Brinsea Octagon 20), you can put the tray and eggs on the scales together.  Then take the eggs out of the tray and weigh the tray alone.  The weight of the eggs without the tray can be calculated using the following simple formula:

(Current weight of eggs) = (Weight of eggs and tray) - (Weight of tray)

Our eggs and tray weighed 59.8 ounces at the beginning of our incubation period and the tray alone weighed 7.3 ounces, so the eggs weighed:

(Current weight of eggs) = 59.8 - 7.3

(Current weight of eggs) = 52.5

The next step is to figure out how much I want the eggs to weigh at the end of the incubation period.  We're aiming for a 13% weight loss, so:

(Goal weight at end of incubation) = (First day weight of eggs) X 0.87

For our eggs, that is:

(Goal weight at end of incubation) = 52.5 X 0.87

(Goal weight at end of incubation) = 45.7

It's also useful to know what our daily weight loss goal is:

(Daily goal weight loss) = (First day weight of eggs) - (Goal weight at end of incubation)

Our eggs need to lose:

(Daily goal weight loss) = 52.5 - 45.7

(Daily goal weight loss) = 0.324

(For those of you who ran away from algebra, be sure to do the subtraction before the division in the equation above.)

Now I'm ready to find out if my eggs are on track with their goal weight loss on a certain day.  After two full days of incubation, I weighed my eggs and tray again, subtracted out the weight of the tray, and got a new weight of 51.8 ounces.  Did I have the humidity set right?

First, I calculate the goal weight loss for the day:

(Goal weight loss on a certain day) = (Daily goal weight loss) X (Days since incubation started)

For my eggs:

(Goal weight loss on day 2) = 0.324 X 2

(Goal weight loss on day 2) = 0.648

Next, I figure how much the eggs should weigh now:

(Goal weight on a certain day) = (First day weight of eggs) - (Goal weight loss on a certain day)

For my eggs:

(Goal weight on day 2) = 52.5 - 0.648

(Goal weight on day 2) = 51.85

Weighing eggs to check humidityIf you remember, my eggs weighed 51.8 ounces on day 2, so if anything they've lost just a hair too much weight.  I had let the incubator's percent humidity drop down into the high 30s that morning since it ran in the low 50s the first day, but it looks like I need to refill the well or close the vent.

I hope this math doesn't look daunting!  I promise, it's simple arithmetic, and weighing your eggs every two or three days during incubation should increase your hatch rates.

Our chicken waterer never spills or fills with POOP.

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It looks like your scale units only go to .1 ounces. Usually the actual accuracy of a scale is less than the smallest unit on a scale so often a scale that says .1 ounces only has an accuracy of .2 or .3 ounces. Therefore there is absolutely no way you could infer that your eggs lost an extra .05 ounces. It is very easy with math to carry the units farther than your scale can actually measure. check the accuracy of the scale on some other objects and look up what the manual says. Most home scales have not only the problem of not going out to the number of places we want but also having too high of a variability between different times measuring. Having used different postage and cooking scales it took me about 10 brands to find one that was accurate to 1 gram (most were off by at least 15g) I used a laboratory grade scale to test the home scales.
Comment by Anonymous late Friday morning, May 6th, 2011

Excellent point! I was actually thinking about significant figures and knew I was ignoring them as I did these calculations. On the other hand, after the first couple of days, that lack of accuracy becomes less important because the amount of weight lost will be higher, making a 0.2 or 0.3 ounce loss of accuracy no big deal. Within the first week, you should be able to see a clear trend as your egg weight continues to be below weight, above weight, or right on target.

What I have started wondering about this calculation, though, is whether I should be dividing the goal weight loss by 21 days or by 18 or 19. My weight loss seemed to be consistently more than it was supposed to be even though I was keeping the humidity on target, and then I realized that around day 19, I'll be increasing the humidity drastically to prepare for hatch, which means that the egg won't lose much more weight. So I might revisit these calculations later, especially if I can find more data on weight loss over time!

Comment by anna late Sunday evening, May 8th, 2011

Thanks for posting this! It was very helpful and clear enough for even me to figure out! Aloha!


Comment by Tonya in the wee hours of Sunday night, January 23rd, 2012
I'm so glad I could help! I figured I wasn't the only one who could use some pointers....
Comment by anna at teatime on Friday, January 27th, 2012

Very clear information thanks for posting, I am also using a Brinsea OCT20 so using the tray to weigh the eggs is definitely convenient. In regards to the # of day for chickens it would be 18 days, for me since I just put duck eggs in my incubator a couple of references I have say 14% weight loss by day 25, after which humidity goes up during lockdown for the last 3 days.

Comment by Clint Saturday night, April 21st, 2012

Clint --- That's what I decided too, eventually --- that I wanted 13% weight loss by day 18. I started getting really good hatches once I figured that out!

Good luck with your duck eggs! I've got some chicken eggs pipping as I type. :-)

Comment by anna early Tuesday morning, April 24th, 2012

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