Varroa mite threshold calculator
Turn your alcohol wash or sugar shake count into mites per 100 bees, and find out whether your colony needs treatment now, using the Honey Bee Health Coalition’s 2026 thresholds for each season.
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Varroa mite threshold calculator
Mites per 100 bees1%See resultHow to use the varroa mite calculator
- Take a sample of about 300 bees, roughly a level ½ cup, from a frame in the brood nest. Make sure the queen isn’t on it.
- Wash or shake the sample and count the mites that come off.
- Enter your count, and the number of bees if you counted them.
- Choose your colony’s seasonal phase. The calculator compares your result with the Honey Bee Health Coalition’s threshold for that phase and tells you whether to treat, plus what to do next.
Varroa treatment thresholds by colony phase
The thresholds come from Table 1 of the Honey Bee Health Coalition’s Tools for Varroa Management, 9th edition (June 2026). It’s the most widely used varroa guide in the US, written with bee researchers and extension specialists.
| Colony phase | What’s happening | Treat promptly at | Mites in a 300-bee sample |
|---|---|---|---|
| Dormant | Bees clustered, little or no brood | 1% or more | 3 or more |
| Population increase | Spring buildup | 1% or more | 3 or more |
| Peak population | Colony at its largest | 2% or more | 6 or more |
| Population decrease | After harvest, raising winter bees | 2% or more | 6 or more |
These thresholds are lower than in earlier editions of the guide. The 2022 edition used 2–3% for most phases. If you learned older numbers, these are stricter.
The decrease phase in late summer and fall matters most. That’s when colonies raise the long-lived winter bees, and the HBHC calls the mite level at the start of this phase critical for winter survival. Test before the colony clusters for winter, too.
Alcohol wash vs sugar shake
- Alcohol or soap wash: the method the HBHC recommends. It’s the most accurate, but the roughly 300 bees in the sample die.
- Powdered sugar shake: the bees survive, but the HBHC rates it less reliable, with more variation in counts. Humidity or a strong nectar flow can make sugar and mites stick to the bees.
Sticky boards, drone brood checks, and looking for mites on adult bees are less reliable. The HBHC doesn’t recommend relying on them to decide whether to treat. A mite testing jar belongs on your list of essential beginner equipment.
Why the calculator projects future mite levels
The HBHC notes that uncontrolled mite populations can double monthly. The “if untreated” lines on the result card apply that doubling to your current count, to show how fast a level just under the threshold can become a problem. It’s a rough illustration, not a forecast. Actual growth depends on brood, season, and mites arriving from other colonies.
What to do if you’re over the threshold
Treat promptly with a registered varroa product that suits the season and temperature, and follow the label exactly. Some treatments can’t be used with honey supers on, and some only work in certain temperature ranges. Then test again to confirm the treatment worked. The HBHC suggests a post-treatment count under 2%. If the count is still high, use a different treatment without delay. Our beekeeping guide for beginners covers how mite monitoring fits into your first year, and our guide to winter colony care covers the broodless winter treatment window.
Common questions
How many mites per 100 bees is too many?
Under the Honey Bee Health Coalition’s 2026 guide, treat promptly at 1 mite per 100 bees (1%) or more in the dormant and population increase phases, and 2% or more at peak population and during the fall decrease.
How do I calculate mites per 100 bees?
Divide the number of mites you counted by the number of bees in the sample, then multiply by 100. For example, 12 mites in 300 bees is 12 ÷ 300 × 100 = 4%.
How many bees are in half a cup?
About 300. The HBHC uses a lightly packed ½ cup of bees from the brood nest as its standard sample. Using fewer than 300 bees makes the result less accurate.
How often should I test for varroa mites?
Monthly from the start of spring buildup, or at least four times from peak population into the fall decline, plus after every treatment to confirm it worked.