Mite Wash Calculator: Convert Your Mite Count to Infestation Rate

You did an alcohol wash. You counted the mites. Now you need to know what the number means.

Use this simple formula to convert your raw mite count into an infestation percentage and compare it against the seasonal treatment threshold.

TL;DR

A valid mite count sample requires approximately 300 bees from the brood nest for statistically reliable results
Alcohol wash is 15-20% more accurate than sugar roll for detecting mite infestation levels
The calculation is: (mites counted / bees in sample) x 100 = infestation percentage
A 2% threshold triggers treatment in spring/summer; 1% is the fall action threshold
Count at least once per month during active season; increase to every 2 weeks if levels are near threshold
Log every count in VarroaVault to build a trend dataset that shows whether populations are rising or stable

The Calculation

Infestation rate = (Mites counted ÷ Bees in sample) × 100

Quick Reference Table, 300-Bee Sample

|-------------|-----------------|---------------------|------------------------|

| 0-1 | 0-0.3% | Low | Low |

| 2-3 | 0.7-1% | Low, monitor | At/near threshold |

| 4-5 | 1.3-1.7% | Below threshold | Above threshold, treat |

| 6 | 2% | At threshold, treat | Above threshold, treat |

| 7-9 | 2.3-3% | Above threshold, treat | Above threshold, treat |

| 10-12 | 3.3-4% | High, treat now | High, treat now |

| 15+ | 5%+ | Very high | Very high |

Thresholds:

Spring and summer: Treat at 2% (6+ mites per 300-bee sample)
Late summer and fall (August onward): Treat at 1% (3+ mites per 300-bee sample)

Quick Reference Table, 100-Bee Sample

If you only collected 100 bees (small colony or limited access):

| Mites Found | Infestation Rate |

|-------------|-----------------|

| 1 | 1% |

| 2 | 2% |

| 3 | 3% |

Note: 100-bee samples are less statistically reliable. At borderline threshold values (1-2%), consider repeating with a larger sample before making a treatment decision.

What to Do With Your Result

At or above threshold: Log the count in VarroaVault and get a treatment recommendation based on your season, available treatments, and rotation history.

Below threshold but within 0.5% of it: Recount in 2-3 weeks. Mite populations can move from 1.5% to above threshold within 4 weeks during active brood season.

Significantly below threshold: Standard monitoring schedule. Recount next month.

Post-treatment count: Calculate efficacy: ((Pre-count − Post-count) / Pre-count) × 100. Below 90% efficacy requires rotation or application review.

Accuracy Notes

Alcohol wash gives the most reliable results. Sugar roll typically reads 15-20% lower than actual infestation. If you used sugar roll and got a result near the threshold, consider confirming with alcohol wash before making a treatment decision.

FAQ

What does 2% mean on a mite wash?

2% means you found 2 mites per 100 bees, or approximately 6 mites in a 300-bee sample. This is the spring and summer action threshold. At or above 2%, treatment is recommended to prevent mite population buildup that could damage your colony's winter population or current production.

How many bees should I have in a mite wash sample?

300 bees is the standard sample size, approximately half a cup by loose volume. This gives statistically reliable results. You can work with 100 bees for small colonies, but the confidence interval is wider and decisions close to threshold should be rechecked with a larger sample when possible.

What if I don't know exactly how many bees I collected?

Estimate based on volume: a level half-cup of bees loosely packed is approximately 250-350 bees. If you're unsure, note the uncertainty. For a result well above or below threshold, the uncertainty doesn't change the action. For a result right at threshold, collect a second sample with a more careful count.

How soon after treatment can I run a post-treatment mite count?

Wait 2-4 weeks after the treatment ends before running a post-treatment count. Counting too soon (within a week of treatment removal) may show mites still dying or emerging from the last brood cycle. Waiting 2-4 weeks allows emerging bees from brood that was capped during treatment to fully emerge and any surviving mites to become detectable in a new count.

What should I do if my mite count results seem unusually high or low?

If results seem surprising, repeat the count within 1-2 weeks before making a treatment decision based on a single outlier result. Confirm you sampled from the brood nest center (not outer frames), used the correct sample size (approximately 300 bees), and shook vigorously for the full 60 seconds. Consistent sampling technique is the most important factor in count accuracy.

Can I count mites from a sticky board instead of doing an alcohol wash?

Sticky board counts measure mite fall rate over 24-72 hours, which correlates with infestation level but is not a direct measure of infestation percentage. Sticky board results cannot be converted to an accurate percentage without calibration, and they are less reliable than alcohol wash for treatment decisions. Use sticky boards for general population monitoring but rely on alcohol wash counts for threshold decisions.

Sources

American Beekeeping Federation (ABF)
USDA ARS Bee Research Laboratory
Honey Bee Health Coalition
Penn State Extension Apiculture Program
Project Apis m.

Log Every Count, Every Time

VarroaVault calculates your infestation rate and threshold comparison automatically when you enter your mite count. No math required, just the data. Start your free trial and track your first count today.

Get Started with VarroaVault

An alcohol wash gives you the number. VarroaVault turns that number into a decision. Log your count, get an instant threshold comparison, and build a monitoring history that shows you whether mite levels are rising or stable across your entire operation. Start your free trial at varroavault.com.