Pollen Count Scale: What Low, Moderate, High, and Very High Mean
A pollen count measures how many pollen grains are floating in the air, reported as grains per cubic meter (grains/m3). Certified stations in the AAAAI's National Allergy Bureau (NAB) pull air across a sticky surface with a Burkard or Rotorod sampler, then identify and count the grains under a microscope. Each day's number reflects roughly the past 24 hours of air.
Those raw numbers are sorted into a five-step scale: None, Low, Moderate, High, and Very High. The catch is that the thresholds differ by pollen type, because trees release far more pollen by volume than grass or weeds. The same "High" label means very different grain counts depending on what is actually in the air.
What Low, Moderate, High, and Very High mean
The same word describes very different air by pollen type: "High" is ~90 grains/m³ for tree but only ~20 for grass.
What Low, Moderate, High, and Very High mean
For tree pollen, Moderate begins around 15 grains/m3, High around 90, and Very High at 1500 or more. Grass is far more potent per grain, so its bands sit much lower: Moderate at 5, High at 20, and Very High at 200. Weed pollen, ragweed included, falls in between, with Moderate at 10, High at 50, and Very High at 500 (NAB thresholds).
What matters for you is the band, not the raw number. High or Very High means most allergy sufferers notice symptoms even with brief time outdoors, and sensitized people should limit exposure and pre-medicate. Low to Moderate usually only bothers the most sensitive.
A measured count is not a forecast
A count is a lab result: a counter tallies grains from a station slide, so it describes air that has already been sampled. A forecast is a prediction, modeling tomorrow's levels from recent counts plus weather and plant timing. Because one is a measurement and the other an estimate, a forecast and the actual count for the same day can disagree (per the NAB and Allergy & Asthma Network).
How weather moves the count
Warm, dry, windy days lift the count, since there is no moisture to weigh grains down. Rain usually washes pollen out for temporary relief, though a downpour hitting peak grass or weed pollen can burst grains into smaller fragments and briefly worsen symptoms. Many pollens, trees especially, release in the morning, so counts climb through the morning and peak around midday (per AAFA). Pushing outdoor activity to late afternoon, or to the calm right after a steady rain, usually catches the count near its daily low.
Where "High" begins, by pollen type
tree pollen to reach High
AAAAI NAB
grass pollen to reach High
AAAAI NAB
weed pollen to reach High
AAAAI NAB
Fewer grass grains reach “High” than tree grains — the scale is calibrated per allergen.
Check your local pollen forecast
Pollen seasons vary sharply by region. These metros see some of the worst pollen pressure — check the current forecast for each, or look up any US city on the pollen count hub:
- Atlanta, GA pollen count — Spring tree counts here routinely reach the 'Very High' band — the scale in action.
- New York, NY pollen count — Tree, grass, and ragweed each push counts into the high range here in turn.
- Houston, TX pollen count — Gulf warmth keeps grass and weed counts elevated much of the year.
- Chicago, IL pollen count — Great Lakes grass and a heavy Midwest ragweed season test every level of the scale.
- Phoenix, AZ pollen count — A dry climate where wind-blown counts spike fast on gusty days.
- Los Angeles, CA pollen count — Mild year-round growth keeps a steady baseline punctuated by tree and grass spikes.
Frequently asked
- How is a pollen count measured?
- Certified National Allergy Bureau stations sample air with a Burkard or Rotorod sampler, then count the grains under a microscope. The result is reported as grains per cubic meter of air over about 24 hours.
- What counts as a high tree pollen count?
- For trees, High begins around 90 grains/m3 and Very High at 1500. Trees release the most pollen by volume, so their thresholds are far higher than grass or weeds.
- Why is the grass pollen scale so much lower?
- Grass pollen is more potent per grain, so its bands are lower: Moderate at 5, High at 20, and Very High at 200 grains/m3. A grass count that looks small can still floor a grass-allergic person.
- What is a high weed or ragweed count?
- Weed pollen, including ragweed, reaches High around 50 grains/m3 and Very High at 500. Moderate starts near 10.
- Is a pollen forecast the same as a count?
- No. A count is a measurement of air already sampled; a forecast predicts upcoming levels from recent counts plus weather. They can disagree for the same day.
- What weather raises the pollen count?
- Warm, dry, windy days raise it. Rain usually lowers it temporarily, and counts tend to climb through the morning and peak around midday.
More pollen & allergy guides
- Ragweed Allergy: Season, Symptoms, and Where It's Worst
- Hay Fever (Allergic Rhinitis): Causes, Seasons, and Relief
- Pollen Allergy Relief: What Actually Works
- Grass Pollen Allergy: Season, Triggers, and Relief
- Tree Pollen Allergy: Season by Region and the Worst Trees
- Allergy Season Calendar: When Each Pollen Peaks by Region
- Cedar Fever: Texas Mountain Cedar Season, Symptoms, and Relief
- Thunderstorm Asthma: How Storms Trigger Sudden Allergy Attacks
- Oral Allergy Syndrome: Why Pollen Makes Certain Foods Itch
- Mold Allergy: Outdoor Spore Season, Symptoms, and Relief
- Allergies vs. a Cold: How to Tell the Difference
- Allergy Immunotherapy: Shots, Tablets, and Long-Term Relief
- Allergy Testing: Skin Prick, Blood Tests, and What Results Mean
- Kids' Allergies: When They Start, Symptoms, and Safe Relief
- Winter Allergies: Indoor Triggers, Symptoms, and Relief
- Fall Allergies: What Triggers Them and When They Peak
- Dust Mite Allergy: Symptoms, Triggers, and How to Reduce Exposure
- Pine Pollen: Why the Yellow Dust Isn't Your Real Allergy Trigger
- Pollen Calendar: When Tree, Grass, Weed, and Mold Seasons Start and End
- Pollen count by city