Incubating Chicken Eggs: How Many Eggs Do I Need? (Let’s Do The Math Together)

Blue Americana Chick - Rose Hill Farm
Day-old Americana chick (Photo: Rose Hill Farm)

When it comes to hatching chickens, you know the old saying “Never count your chickens before they hatch!”

And that is because it seems like such a simple thing to do – incubate some chicken eggs – but in reality there are dozens of small things that all have to go just right in order to realize 12 chicks out of 12 eggs.

What I hear most often goes something like: “I want 6 hens (or 3 hens or 8 hens) so how many eggs do I need to set?

This Doesn’t Have To Be Complicated

Whether you are ordering eggs from a hatchery or setting some of your own, deciding how many eggs you should set doesn’t have to be complicated.   There are some simple guidelines you can follow to help ensure your hatching experience lets you end up with the hens that you want.

Let’s run through 4 of the most important considerations for determining how many eggs you should incubate.

1.  How many new hens do you want?

The first thing to consider when hatching eggs is your end goal:   How many hens do you want?  

If you want 6 hens, there is probably no need to set 2 dozen eggs, but you might need to set more than 1 dozen.

How do I know that? I’ll show you how I got to this conclusion by the end of the post.  Read on. . . .

Eggs typically hatch at a 50:50 sex ratio. That means only half of the eggs will turn into hens and the other half will be roosters.   This is not a guarantee, just a law of averages. 

So what does that mean? Well, on average, half of the chicks in any hatch will be female.  But in reality you may end up with a hatch that is 75% roosters and only 25% are hens. It happens. That what an average means. If you did 100 hatches, and counted out all the chicks, half would be hens. But in any given hatch, you could get more or less hens, and it is just the luck of the draw when eggs are randomly collected for hatching.

Barred Rock Chicks in a brooder cage at Rose Hill Farm
On average, half of the chicks will be hens, and half roosters (Photo: Rose Hill Farm)

The point is, while not certain, on average, half of the chicks that hatch will be female.  Therefore the absolute minimum number of eggs you need to set is twice the number of hens you want to end up with.

If you want 2 hens, the absolute minimum set is 4 eggs.

If you want 6 hens, the absolute minimum set is 12 eggs.

If you want 10 hens, the absolute minimum set is 20 eggs.

And so on.

2. Hatching rates

The next thing you need to factor in is that not all the eggs will hatch each time, just like in the saying. You may have put 12 eggs into the incubator, but you may not end up taking any chicks out at all.

You can minimize wasting time with infertile and damaged eggs by candling them prior to setting.  Candling is where you use a strong light to examine the inside of the egg to see a formed yolk and the outside of the egg for any cracks or fissures.   Eliminating any non-starters saves time and effort.

But even once you have eliminated infertile and cracked eggs, hatching rates may still vary.  This is because incubation involves a complex set of factors that include temperature, humidity and turning rates for success.

There are also breed-specific issues that affect hatching rates like shell strength and other genetic factors.  Hard-shelled breeds, like the Marans, may require higher humidity during “lock down” to get good hatching results.  You can often pick up tips for hatching from researching the breed chickens that you keep.

Mixed Hatching Eggs - Rose Hill Farm
Different breeds of chickens can have different hatching rates based on shell quality and thickness.
These eggs come from Barred Rocks, Olive Eggers, Americanas and Marans (Photo: Rose Hill Farm)

Shipped eggs, as in those sent by mail or courier from a breeder or hatchery, may also have reduced hatching rates. The jostling and disturbance that happens during shipping, as well as the temperature and humidity, can all impact your results. So while a breeder might be getting very high hatching rates (like 95% or better) you may see reduced hatch rates (more like 75% or sometimes as low as 50%). The most critical thing with shipped eggs is to ALWAYS let the eggs settle for 24 hours before setting them in the incubator.

So what should you do about hatching rates?

To compensate for the factors that influence hatching rates, it is always a good idea to add in some extra eggs to buffer for these effects.   But how many more eggs should you incubate?

Personally, I go with a minimum of 10-15% more eggs in the hatch, unless I am dealing with shipped or difficult to hatch eggs.  I would add 25-50% more eggs if dealing with shipped or difficult-to-hatch breeds respectively.  What does this look like?

If you want 6 hens – adding 10-15 %  onto the 12 egg minimum results from above results in setting 13 -14 eggs for the hatch.

If you want 6 hens from shipped eggs or challenging breeds – adding 25-50% onto the 12 egg minimum results in setting 15- 18 eggs.

 3. Incubator limits

In all the excitement that starts to set in when getting ready to order eggs from a hatchery or gathering your own eggs to set, don’t forget that incubators (and broody hens – go to #4 for that) have practical limits when it comes to having successful hatches.  

While it can be tempting to try and find a way to cram just a few more eggs into a batch, the results can be disastrous.  Improper temperature, humidity or turning can lead to really disappointing results. 

And well it is always tempting to blame the egg supplier (the breeder, hatchery, or the flock rooster!) for poor hatch results, it can also be the result of poor decision-making when it comes deciding how many eggs to set. As they say: “Know Your Limit – Play Within It!”

Incubator types

Incubators come with a maximum batch size clearly defined in their operations manuals. It’s always best to follow the manufacturer’s guidelines for how many eggs can be set.  Trying to boost egg numbers by cramming in an extra egg here or there can mean that the whole batch suffers.

Luckily, there are incubators in every size imaginable, from 7 egg sets all the way into the hundreds of eggs for the big cabinet incubators.  It is extremely challenging to raise a single chick by itself. Chicks thrive when they have other chicks for company, encouragement and warmth. So even small incubators should accommodate at least 6 eggs. I would be wary of spending money on anything smaller than that.

There are also many options to consider from less expensive incubator models that simply hold constant temperature, through to ones that have automatic turners and all the way to fully automated (temperature, humidity and turning) models.

I have two fully automated Brinsea models (Maxi II – 14 eggs and Ovation – 28 eggs), as well as a Hovabator with an automatic turner (but no humidity controls). But there are a wide range of options in the Brinsea and Hovabator brands, as well as other brand names with good success rates. Choose the one that suits your needs and budget (check out these and other useful chicken products on my Shop for Products page)

4. Broody Hen Limits

If you have a broody hen willing to incubate eggs for you, you still need to consider the limits of her incubating capacity!

If you give her too few eggs, she may be tempted to abandon the nest. Too many eggs and there might not be enough hen to go around. She may still attempt to hatch them all, but if there are too many then you risk that none of them will stay sufficiently warm to develop and hatch.

Silkie hen brooding chicks - Rose Hill Farm
Broody Silkie Hen with a Barred Rock chick (Photo: Rose Hill Farm)

My rules for giving eggs to broody hens include consideration of:

Size and Breed of the Hen:

A small Silkie hen cannot incubate 6 large breed eggs very easily (at least my Silkie hens are too small for this) whereas I have had a Barred Rock hen sneak off and sit on a batch of 14 eggs and successfully hatch 12 of them.   Think about how big your hen is and whether she can fluff herself over the number of eggs you give her. If not, then it is usually a good idea to scale down the number to increase your chances of a good hatch.

Size and location of the nest box:

 The comfort and fit of the nesting box is a critical factor in success.  The box should be big enough to allow the hen to comfortable sit in her nest, turn around, and stand up easily, but not be so big that she has trouble staying warm.

It should allow the hen to get in and out easily so that she doesn’t accidentally break an egg (it should also allow the chicks to get in and out easily so one doesn’t become trapped away from the hen).

The nest box should be in a sheltered location that protect the hen from the elements and from other hens. Other hens are very happy to go in and continue to lay eggs for the broody hen to manage, but that can lead to an overcrowded nest and broken eggs.

It’s a good idea to provide adequate bedding in the nest box to cushion the eggs while the hen is turning and sitting on them. Wood shaving, straw, grass clippings and other types of bedding can help the hen have better hatching results.

Time of year:

It is far more critical to set fewer eggs with a broody hen in winter, or during cold shoulder seasons, than in summer when the ambient temperature is warm, that is, if you are lucky enough to have a broody hen in the winter. To my surprise, I have had several of my Silkie hens become broody in the winter, which creates an opportunity to consider a hatch. 

When in doubt, Test the numbers:

If you are still in doubt about how many eggs to let a hen sit on, you can always test your ideas using marked infertile eggs, fake eggs or even golf balls.  The idea is to give the hen the number of eggs you hope for her to hatch and watch how she manages for a day or two. 

If she is able to sit comfortably on all the eggs and doesn’t abandon the nest, then go ahead and swap out the test eggs for the real ones you hope to hatch.  But if you see that she is not able to properly cover the nest of eggs, then reduce the number down for better hatching success.

What does all that mean in practice for using broody hens to hatch eggs?

 On my farm, that translates into the following broody hen limits:

Silkie hen hatching Silkie eggs: up 6 or 8 depending on the size of the hen

Silkie hen hatching regular eggs: only 2-4 depending on the size of the hen

Barred Rock, Americana or Marans: 6-14 eggs depending on my hatching goals

Want Help With The Math?

I’ve put together a handy table that calculates out the number of eggs you need to incubate based on the number of hens you want.

Click HERE for you free copy of the spreadsheet where you can add your own number and have the calculator generate your specific results.

How Many Eggs Should I Set Chart - Rose Hill Farm
visit the website: Rose Hill Farm

Looking for Resources?

Check out my Shop for Products page to find descriptions of the products I like to use, or use these quick links to products mentioned in this post.

Incubators: You can search for Chicken Egg Incubators to see the all the models that are available. The ones I use are: Brinsea Maxi II Ex, Brinsea Ovation 28 Ex, Hovabator Genesis with automatic turner, Hygrometers

Candler: You can search for candling equipment. The one I use is a Brinsea High Intensity Candler.

Chick Brooding equipment: You can search for chick brooder equipment. I like to use a rabbit or small animal cage, Heat mat, and a plastic igloo as a chick house.

Books: The Small Scale Poultry Flock