Connect with us

converting watts to milliamps

Discussion in 'Electronic Basics' started by Carl Farrington, Dec 13, 2003.

Scroll to continue with content
  1. Hi there,

    Please could someone explain to me how to convert watts into milliamps? I
    want to compare the power usage characteristics of two devices (one is a
    2.5" hard disk, the other is an IDE Flash Disk) but one manufacturer lists
    usage in watts, the other in milliamps!


    Carl Farrington
  2. Amps = watts/volts
    divide the result by 1000 for mA
  3. thank you!
  4. Assuming we're talking DC here (the AC formulae are slightly
    different): Ohm's Law gives you everything you need.

    P = IE, where P is power in Watts, I is the current drain in Amps,
    and E is the voltage involved.

    Taking this a step further, we get I = P / E

    So: As an example, assume a 12V fan draws 4 watts of power. That's
    4 over 12, which gives a current drain of about 0.333A, or 333mA.

    We can double-check this by finding the resistance, and using
    Ohm's Law again: R = E / I. Since we now know I, we can find that
    R = 12 / 0.333 = about 36 ohms.

    Now that we know resistance, we can use the formula P=I-squared
    times R to find the power figure: P = .333 squared times 36 = 3.99
    watts. Pretty close, heh?

    You can also simply do P = IE, or .333 times 12 = 3.996.

    Hope that helps. ;-)

    Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
    (Known to some as Bruce Lane, KC7GR)
    kyrrin a/t bluefeathertech d-o=t c&o&m
    Motorola Radio Programming & Service Available -
    "Quando Omni Flunkus Moritati" (Red Green)
  5. Ian Stirling

    Ian Stirling Guest

    You may want to look at the detailed datasheets, and work out just
    what your usage will be.
    Active, sleep, read/write, spinup, ...
  6. KP

    KP Guest

    another way is to go to and download 'Versaverter' saves
    the brain somewhat
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day