No published figure tells you how much seed your feeders will use: it depends on which birds come, how many, the season and what else they find to eat. So this calculator starts from what you can measure: how many days a bag lasts, or how much you add at each refill. It works out seed per day, bags per period and, with your own prices, the cost. Only the calendar periods are pre-filled, and nothing you type leaves your browser.
1. Your foods — one row per kind of bag; leave unused rows empty.
Don't know how long a bag lasts? Work it out from your refills
Weigh what you pour in, or count scoops of a known weight.
2. Period
How to measure your rate
- Write the date on the bag when you open it, and note its weight from the label.
- Feed as you normally do. Seed lost to squirrels, spills or mold counts too; see squirrel-proof bird feeders and bird feeder types.
- Note the date the bag runs out and enter the number of days between the two dates.
- No bag finished yet? Open the refill box above: enter how much you pour in each time and how many days pass between refills.
- Measure again when the season changes. Feeder use is not steady through the year (see below), so a rate from November won't fit May.
The formula
| Step | Formula | What you enter |
|---|---|---|
| Seed per day | bag weight (lb) ÷ days one bag lasts | Both from your own bag |
| From refills | lb per refill × feeders filled ÷ days between refills | Your own refills |
| Seed for a period | seed per day × days in the period | Choose the period |
| Bags to buy | seed for the period ÷ bag weight, rounded up | — |
| Cost per pound | price per bag ÷ bag weight | Your price |
| Cost of seed used | seed for the period × cost per pound | — |
The only built-in numbers are calendar lengths: 7, 30 and 365 days, and the 181 days of the 2026–27 Project FeederWatch season, which runs from November 1 through April 30. The 60-day storage flag and the 60-lb comparison come from the sources discussed below. Prices are never filled in: use your own receipt.
- One bag, with its weight B in pounds from the label.
- Seed per day = B ÷ D, where D is the number of days the bag lasted at your feeders.
- A period of N days needs seed per day × N, rounded up to whole bags; your price per bag turns that into a cost.
- The 2026–27 Project FeederWatch season, November 1 to April 30: 181 days.
- A 60-day window: Texas A&M–Kingsville's advice to quail managers is to buy only as much grain as can be fed in under two months; the calculator flags any bag that lasts longer than 60 days.
Why there is no "typical" amount
How much birds eat varies a lot by size. The Cornell Lab's All About Birds says a chickadee may eat 35 percent of its weight in food each day, a Blue Jay only about 10 percent and a Common Raven about 4 percent. And feeders supply only part of it. In a Wisconsin study, M. C. Brittingham and S. A. Temple found that Black-capped Chickadees at winter feeders got about 21 percent of their daily energy needs there (Journal of Wildlife Management, 1992).
Use also shifts with the calendar. In the same study, feeder use peaked in autumn and was lowest in spring, and air temperature had no measurable effect on it. Project FeederWatch's Chelsea Benson describes more feeder activity as the weather gets colder and natural food gets harder to find, and notes a fall when birds stayed in the woods because natural foods were plentiful. That is why the steps above ask you to measure again each season.
For scale, a University of New Hampshire Cooperative Extension article by Margaret Hagen says one in three North American households puts out an average of 60 pounds of feed a year, while dedicated feeders buy "hundreds of pounds of feed each winter." The calculator shows your yearly figure for comparison.
Buying and storing what you calculate
Knowing how long a bag lasts helps you buy a size that stays fresh.
- Keep food moving: David Bonter of the Cornell Lab says it should pass through the feeder "pretty quickly to prevent mold from forming," and advises against feeders packed to the top in hot, humid weather.
- Store spare seed in a cool, dry place (Bonter), in a metal bin that animals can't get into rather than a plastic bag in the garage (FeederWatch's Emma Greig).
- Hulled sunflower leaves less chaff but spoils more quickly than seed in the shell, so keep it dry (Project FeederWatch).
- Feed nyjer on its own to prevent waste, and in the East avoid mixes heavy in milo, which often goes to waste there (Project FeederWatch).
- Throw out moldy seed, in the feeder or the storage bin (Bonter). Aflatoxin builds up the longer grain is stored, whatever the container, and mold is a strong sign it could be present (Oklahoma State University Extension).
- Buy no more grain than you can feed in under two months; Scott Henke of Texas A&M University–Kingsville gives this advice for quail feed, and the calculator uses it as its 60-day flag.
Cleaning is covered in how to clean a bird feeder; for which seed to buy, see what to feed backyard birds and the season guides for winter and summer.
If you cut back
In another Wisconsin study, Brittingham and Temple found over-winter survival of 69 percent for chickadees with feeders against 37 percent without, with the biggest gap in months with more than five days below −18 °C (about 0 °F) (Ecology, 1988). FeederWatch's Emma Greig adds that birds rarely, if ever, depend heavily on any one food source, since they use many in winter. So if you trim the budget, the coldest spells are when feeders count most. Project FeederWatch shows which birds your seed actually feeds.
Sources
- How much do birds eat each day? — All About Birds, Cornell Lab of Ornithology
- Use of winter bird feeders by black-capped chickadees — M. C. Brittingham and S. A. Temple, Journal of Wildlife Management 56(1):103–110, 1992 (Penn State record)
- Impacts of supplemental feeding on survival rates of black-capped chickadees — M. C. Brittingham and S. A. Temple, Ecology 69(3):581–589, 1988 (Penn State record)
- How to Participate — Project FeederWatch
- Food Types — Project FeederWatch
- The Project FeederWatch Team Answers Your Questions About Bird Feeding (Emma Greig, Chelsea Benson) — Cornell Lab Bird Academy
- Safe Summer Bird Feeding: Q&A With David Bonter — Pat Leonard, Living Bird, Cornell Lab of Ornithology (2014)
- This is Really for the Birds (PDF) — Margaret Hagen, University of New Hampshire Cooperative Extension
- Aflatoxins in Wildlife Feed: Know How to Protect Wildlife, NREM-9021 (PDF) — Oklahoma State University Extension (2021)
- Aflatoxin: What's a Quail Manager to Do? (PDF) — Scott E. Henke, Texas Wildlife, Caesar Kleberg Wildlife Research Institute, Texas A&M University–Kingsville (2017)