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Test5 min read

What are normal radon levels?

By Radon411 Editorial TeamUpdated How we research

Short answer

The average indoor radon level is estimated at about 1.3 pCi/L, and outdoor air normally has about 0.4 pCi/L. Homes vary widely around that, nearly 1 in 15 homes in the United States is estimated to have an elevated level, and even levels below 4 pCi/L pose some risk.

Next step: pick the right test for your home. Which test to use

To read any result against EPA's guidance, see our guide to radon levels.

All outdoor and indoor air has some radon in it, so a normal reading is never zero. Worldwide, average outdoor radon ranges from 5 to 15 , while homes, schools and offices range from 10 Bq/m3 to more than 10,000 Bq/m3.

Normal varies by floor: radon levels are usually higher in basements, cellars and living spaces in contact with the ground. It varies by home too: homes next to each other can have different indoor radon levels, and high levels have been found in every state.

Normal is not a threshold. Congress has set a long-term goal that indoor levels be no more than outdoor levels, and radon can be reduced in most homes to 2 or below.

What to do next: test the lowest lived-in level of your home, with a of at least 48 contiguous hours or a of more than 90 days, and compare the result in the interpreter.

At a glance · 1 min read

The averages

All outdoor and indoor air has some radon in it, so a normal reading is never zero. The average indoor level is estimated at about 1.3 , and about 0.4 pCi/L is normally found in outside air.

Typical radon levels (worldwide figures converted to pCi/L by our arithmetic)
WherepCi/LBq/m3
Average outdoor air (U.S.)0.414.8
Average indoor air (U.S.)1.348.1
Average outdoor air worldwideAbout 0.14 to 0.415 to 15
Homes, schools and offices worldwideAbout 0.27 to more than 27010 to more than 10,000
Show all 4 rows
Read moreA paragraph, 1 min

Congress has set a long-term goal that indoor radon levels be no more than outdoor levels: the aim is indoor air no worse than outdoor air.

In a picture · 1 min read

Normal is not the same as safe

An average is not a threshold. Even radon levels below 4 pCi/L pose some risk, and you can reduce your risk by lowering your radon level. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L.

Scale of radon levels from 0 to 10 pCi/L marking EPA's 2 pCi/L level, where EPA says to consider fixing, and its 4 pCi/L action level, where EPA says to fix the home, with each mark also in Bq/m³.
The average indoor level, 1.3 pCi/L, sits well below EPA's marks at 2 and 4 pCi/L.
Read this figure as text
  • Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
  • 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
  • At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
Read moreA paragraph, 1 min

Radon levels can be reduced in most homes to 2 pCi/L or below. See what is a safe level of radon.

Overview · 1 min read

Elevated levels are common

Nearly 1 out of every 15 homes in the U.S. is estimated to have an elevated radon level, EPA says, and high radon levels have been found in every state. Levels vary greatly from home to home, and homes next to each other can have different indoor radon levels.

Read moreA note, 1 min

At a glance · 1 min read

Two units for the same thing

Radon levels are reported in picocuries per liter (pCi/L) in the United States and in (Bq/m3) in much of the world. A becquerel reading counts the number of atomic transformations per second in a cubic meter of air. One pCi/L equals 37 Bq/m3.

Normal and notable levels in both units (conversions are our arithmetic)
LevelpCi/LBq/m3
Average outdoor (U.S.)0.414.8
Average indoor (U.S.)1.348.1
EPA's consider-fixing mark274
EPA's action level4148
Show all 4 rows

At a glance · 1 min read

Normal by floor

What is normal for a basement differs from what is normal upstairs. Radon levels are usually higher in basements, cellars and living spaces in contact with the ground, and often higher in basements and lower levels.

Where levels tend to run highest
PlaceTypical pattern
OutdoorsQuickly dilutes to very low concentrations
Upper floorsUsually lower than the basement, but not radon-free
Basement and ground-contact roomsUsually the highest in the home

Overview · 1 min read

What a normal reading tells you

A single reading is a snapshot. Because radon levels tend to vary from day to day and season to season, a is less likely than a to tell you your year-round average, and the year-round average is what to compare with these figures. Test the lowest lived-in level so the number reflects where radon is usually highest among the rooms you use.

Read moreA note, 1 min

At a glance · 1 min read

Normal by area

EPA's Map of Radon Zones describes predicted averages by area: areas may average above 4 pCi/L indoors, Zone 2 between 2 and 4, and Zone 3 below 2. Homes with elevated levels have been found in all three zones.

Predicted average indoor levels by EPA zone
ZonePredicted potentialAverage indoor level may be
Zone 1HighestGreater than 4 pCi/L
Zone 2ModerateBetween 2 and 4 pCi/L
Zone 3LowLess than 2 pCi/L
Read moreA paragraph, 1 min

See your county on the radon map, and remember it is a prediction for an area, not a reading of your house.

Questions · 1 min read

Questions about normal radon levels

What is a normal radon level in a house?

The average indoor level is estimated at about 1.3 pCi/L. Individual homes vary widely around it.

What is a normal radon level outdoors?

About 0.4 pCi/L in the U.S., and 5 to 15 Bq/m3 worldwide.

What is a normal radon level in a basement?

Usually higher than the floors above, because basements are in contact with the ground.

Is 2 pCi/L normal?

It is above the average indoor level of about 1.3 pCi/L. EPA recommends considering a fix when the level is between 2 and 4 pCi/L.

Can radon be zero?

No. All outdoor and indoor air has some radon in it.

How common are high radon levels?

Nearly 1 in 15 U.S. homes is estimated to have an elevated level, and high levels have been found in every state.

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