The 50 lb bag is the standard unit of backyard chicken keeping. It is what the feed store stocks, what the prices are quoted in, and what your monthly budget gets measured against. But "how long does it last" is really a math question with one input: how many birds.
A laying hen eats about 1/4 lb of feed per day, which is 1.5 lb per week. So the base formula is simple: days per bag = 50 / (birds x 0.25). One hen: 200 days. Six hens: about 33 days, or roughly a month.
Five worked examples
All examples assume standard laying hens at 1/4 lb per bird per day, mild weather, no free-ranging, and an average feeder with normal waste.
| Flock | Daily use | One 50 lb bag lasts | Bags per month | Cost/mo at $22/bag |
|---|---|---|---|---|
| 4 hens | 1.0 lb | 50 days (7 weeks) | 0.6 | $13.20 |
| 6 hens | 1.5 lb | 33 days | 0.9 | $19.80 |
| 12 hens | 3.0 lb | 17 days | 1.8 | $39.60 |
| 20 hens | 5.0 lb | 10 days | 3.0 | $66.00 |
| 30 hens | 7.5 lb | 6.7 days | 4.5 | $99.00 |
The 6-hen line is the one most backyard keepers should memorize: about a bag a month, about $20 a month in feed. When I tell new chicken people their feed bill will be roughly twenty bucks a month for a starter flock, they are usually relieved. It is the coop, not the feed, that costs real money.
Why your bag might not last as long as the math says
If your real-world usage is way off these numbers, one of these is usually the culprit.
Winter. Cold weather intake rises 15 to 30%. That 6-hen flock that burns a bag a month in spring will chew through 1.2 to 1.3 bags in January. Budget for it; do not be surprised by it.
Feed waste. A cheap trough feeder in the rain can waste 10 to 20% of what you buy. Spilled, rained-on, or trampled feed does not feed chickens. A hanging feeder or a treadle feeder pays for itself fast if you are currently using an open pan on the ground.
Wild birds and rodents. Sparrows can eat a shocking amount of layer feed, and rats eat at night when nobody is watching. If your bag math says 33 days and you are buying every three weeks, watch the feeder for an hour at dusk. You might find the problem has feathers or a tail.
Growing birds. The examples above are for adult layers. A dozen 10-week-old pullets are eating more per bird every week, and broilers at finishing weight eat nearly double a layer's ration. Run the numbers for your actual bird type, not the average.
Treats displacing feed. This one goes the other direction: heavy kitchen scraps and scratch can stretch a bag because the birds eat less feed. Just remember treats should stay under about 10 to 15% of intake, or you will trade feed savings for thin shells and lower production.
Buying strategy: how many bags to keep on hand
For a flock under 10 birds, one bag in the feeder plus one unopened bag in reserve is the right inventory. Feed stays fresh about 2 to 3 months in a cool, dry place (a metal trash can with a lid is the classic setup), so do not stockpile six months ahead unless you have a very large flock. Old feed loses nutritional value and goes musty, and a musty bag is a wasted bag.
For flocks of 20+, watch for bulk pricing. Many feed stores knock 5 to 10% off when you buy 10+ bags, which on a $99/month habit is real money over a year. Just make sure you can store it dry and use it within the freshness window.
Do the exact math for your flock, with winter and free-range adjustments: Chicken Feed Calculator. Enter your bird type, flock size, bag price, and it gives you daily through monthly feed, bags per month, cost, and cost per dozen eggs.
The short answer
One hen eats a 50 lb bag in about 200 days. Divide 200 by your bird count and you have your answer: 33 days for 6 hens, 17 days for 12, a week for 30. Adjust up in winter, down with good pasture, and always fix the feeder before you blame the birds.
Curious how feed intake changes as birds grow from chicks to layers? The week-by-week breakdown is in Chicken Feed Intake Chart by Age.