EMF and EMR Conversion Formulas

by / Monday, 18 February 2013 / Published in EMF/EMR, Environmental Testing, Healthy Building Inspections
Instruments_1862-Alex-Bedroom EMF

How do you convert microwatts per square meter (uW/m2) into microwatts per square centimeter (uW/cm2)?  How many nanoTesla (nT) are in 2.0 milliGauss (mG)?  We’re asked these questions frequently so we’re providing a few common EMF and EMR conversion formulas and conversion charts for your reference.

EMF and EMR Allowable Limits

“What level of EMF and RF are safe?”  This is a really difficult question that has yet to be fully answered by the scientific community. What we do know, and what is clearly presented in the BioInitiative Report, is that there is cause for concern with current levels of exposure in the US. If our government (FCC, OSHA) followed the precautionary principle we would have much more stringent guidelines for EMF (specifically magnetic fields) and RF (radio frequency) radiation.

The RF limits established by the FCC are actually quite complicated because they allow different power densities for each bandwidth. This makes measuring for compliance with FCC guidelines a rather expensive endeavor.

People get their own EMF meters and don’t immediately understand what the numbers on the screen mean. Now you can translate the numbers from your meter into similar units as used by these existing guidelines. Personally, I lean toward the precautionary principle and like using the Building Biology thresholds whenever possible.

Magnetic Field Allowable Levels

Magnetic Field Allowable Levels

How much is too much? That is up to you decide.

RF Allowable Levels

RF Allowable Levels

Magnetic Field Measurement Conversion Chart

Many people get “EMF meters” that only evaluate magnetic fields. The units on the meter are usually nanoTesla (nT) or milliGauss (mG). Healthy Building Science likes to use milliGauss in our EMF Inspection reports. Fortunately it’s as easy as moving the decimal over 2 places!

Magnetic Field Conversion Chart

Magnetic Field Conversion Chart

 

Radio Frequency (RF) Radiation Conversion Chart

The most common RF conversion I run into is for the following: Converting microWatts per square meter to microWatts per square centimeter:

RF Conversion Chart

RF Conversion Chart

Converting Using EMF and EMR Conversion Formulas

The first two relate to electric fields (kV/m & V/m). After that, the next six are for radio frequency (RF) power levels. And the final four are concerned with magnetic fields. The calculations in the charts all revolve around Watts per square meter (W/m2). So to find the other values if you know W/m2, here are the formulas I used to get them:

V/m = √ W/m2 x 377 (Volts per meter = the square root of the product of Watts per square meter times 377)

kV/m = V/m /1,000 (Kilo-volts per meter = Volts per meter divided by 1,000)

mW/cm2 = W/m2 / 10 (Milli-Watts per square centimeter = Watts per square meter divided by 10)

uW/m2 = W/m2 x 1,000,000 (Micro-Watts per square meter = Watts per square meter times one million)

uW/cm2 = W/m2 / .01 (Micro-Watts per square centimeter = Watts per square meter divided by .01)

nW/cm2 = W/m2 / .000,01 (Nano-Watts per square centimeter = Watts per square meter divided by .000,01

pW/cm2 = W/m2 / .000,000,01 (Pico-Watts per square centimeter = Watts per square meter divided by .000,000,01)

A/m = √ W/m2 / 377 (Amps per meter = the square root of the product of Watts per square meter divided by 377)

mG = W/m2 / 23.9 (Milli-Gauss = Watts per square meter divided by 23.9)

uT = W/m2 / 239 (Micro-Teslas = Watts per square meter divided by 239)

nT = W/m2 / 239,000 (Nano-Teslas = Watts per square meter divided by 239,000)

Some other useful conversion formulas are :

mG = (A/m)2 x 15.774059        A/m = √ mG / 15.774059

nT = mG x 100                         mG = nT / 100

A/m = √ nT / 1,577.4059        nT = (A/m)2 x 1,577.4059

V/m = W/m2 / A/m                 V/m = (mW/cm2 x 10) / A/m

A/m = W/m2 / V/m                 A/m = (mW/cm2 x 10) / V/m

 

And some useful predictive (but possibly inaccurate*) conversions between electric, magnetic, and power units:

V/m = √ nT x 90,103              V/m = √ mG x 9,010.3

nT = (V/m)2 / 90,103              mG = (V/m)2 / 9,010.3

W/m2 = (V/m)2 / 377             mW/cm2 = (V/m)2 / 3,770

W/m2 = (A/m)2 x 377             mW/cm2 = (A/m)2 x 37.7

*Since power flow, electric fields, and magnetic fields are all perpendicular to each other, like the hub, spokes, and rim of a bicycle wheel respectively, these results may not perfectly correlate with measured field readings, depending on the geometry of wiring configurations and measuring distances.

Also, in the conversion tables, you will find some numbers abbreviated with an exponential notation. For instance, 2.41E-07 is really 2.41 times 10 to the negative seventh power, or 0.000000241. And 7.63E+08 is really 7.63 times ten to the eighth power, or 763,000,000.0.

Mind your digits and decimals!

 EMF and EMR conversion formulas and some commentary above provided by Bob Dahse and GeoPathFinder.com, and Rob Metzinger and SLT.co. Thank you both!

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7 Responses to “EMF and EMR Conversion Formulas”

  1. Cameron Das says :

    Hello Dietmar (again),

    I described the equation for calculating the magnitude of magnetic fields, but the equation should still hold true for RF radiations, as well. Sorry for any confusion.

    RF meters typically combine all axis values automatically, so please do look to your RF meter’s instruction manual to find how enable the option.

  2. Cameron Das says :

    Hello Dietmar,

    From what you described, it seems that you have a triaxial gaussmeter that only reads each axis individually.

    To get the overall combined magnitude of the magnetic field, use this equation:
    Magnetic magnitude = Sqrt (X^2 + Y^2 + Z^2)
    Where X, Y and Z are the measurements of each axis.

    Since magnetic fields are frequently variable, it is difficult to take the three independent axis measurements simultaneously manually, so most higher priced triaxial gaussmeters perform this calculation automatically for the user.

    Hope this helps!

  3. Cameron Das says :

    Hello Chris,

    There is more to take into account for in generating a consistent magnetic field than just the wattage (current) that is running through the copper wire.

    The earth’s magnetic field is a static DC (direct current) magnetic field, like a bar magnet. This kind of magnetism typically has something to do with the predominate direction of the electrical polarities of the atoms that make up ferric (iron containing) metals. You can buy bar magnets from Radio Shack or the like, but since they are localized the strength of the field will vary greatly in a short distance. At one distance you might measure 0.5mG, but measure 1 inch off in nearly any direction, and the number will be much higher or much lower.

    You could create a weak bar magnet by taking a battery, an iron rod (even a 10penny nail will work), a wire and a small light bulb. By wrapping the wire around the iron rod in a spiral fashion and connecting the wire to a light and finishing the circuit back to the battery. The electrical flow will induce upon the iron rod and force some of the ferric atoms to re-align over time and create a weak bar magnet out of the iron rod. After removing the iron rod after some time has passed, you’ll be able to pick up paperclips and move the points of a magnetic compass. There is no way to predict how strong that bar magnet will be, however.

    Typically when people are concerned about magnetic fields in regards to health concerns, they are concerned with AC (alternating current) magnetic fields. Generating an AC magnetic field takes more engineering and I won’t recommend you try it unless you become more familiar with electricity, magnetism and basic electronics or hire an engineer to make a device for you.

    For what purpose are you looking to produce a 0.5 mG magnetic field? If you describe the application I might be able to direct you towards a solution.

  4. Chris says :

    I’ve been searching and searching but cannot find the answer to my question…maybe you can help me…I’m trying to create a magnetic field on a copper wire, with a battery, which is equal to the magnetic field of Earth, which is about 0.5 gauss…yet I do not know how many watts of current I need to produce from a battery to create a magnetic field of 0.5 gauss on a copper wire…can you tell me how much wattage I need to produce from a battery to replicate Earth’s magnetic field? Thanks!

    – Chris

  5. Alex Stadtner says :

    Is this a question?

    If it was, Building Biologists generally measure RF using a tri-axis meter so as to get an accurate representation of ambient EMR conditions.

    However, if you’re looking for a source you can also look axis-by-axis and see where the predominant source of RF is coming from for a particular space.

    Hope that helps you in measuring radio frequency radiation,
    Alex

  6. dietmar doehring says :

    i have an rf meter which measurement is correct i have 3 axis x y anz.

    to i measure all three at the same time

  7. Alex Stadtner says :

    A special thanks to Dustin Mapel, Antioch College Co-Op student extraordinaire, who helped pull together these EMF resources!

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