# DigiKey's Online Calculators

Many times DigiKey customers call in or chat looking for help finding parts with certain specifications they cannot find on our site. Many times we find the customer is just not looking at the right specification. Capacitors are a prime example of this. On the Digi-Key sight you will find items listed as pF(picoFarad) or µF (micr Farad), however in the real world you may find thing in nF(nano) or just in F. This is where the DigiKey calculators can come in handy. Using the Capacitance Conversion Calculator you can convert from one value to another with the press of a button.

The Battery Life calculator is another one many of our customers find useful. Generally, battery life is calculated based on the current rating in milli Ampere Hours, which is abbreviated as mAh. Ampere is an electrical unit used to measure the current flow towards the load. The battery life or capacity can be calculated from the input current rating of the battery and the load current of the circuit. Battery life will be high when the load current is less and vice versa. The calculation to find out the capacity of battery can be mathematically derived from the following formula:

Battery Life in Hours (h) = Battery Capacity in Milli amp hours (mAh) / Load Current in Mill amps (mA) * 0.70

*Note: The Factor of 0.7 makes allowances for external factors which can affect battery life.

The Resistor color code Calculator is also another tool that can help you identify the resistance of a through hole resistor on your board. The Digi-Key calculator can do 4, 5 or 6 band resistors.

Here is also the standard 4 band color chart.

There are also many other useful calculators that help our customers available.

You can also use DigiKey’s calculators as a quick and easy-to-use resource and don’t forget to bookmark the page for future use.

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In your discussion of the Battery Life calculator you say mAh is current rating in milli Ampere per hour. This is incorrect and should read milli Ampere hour (commonly called “milliamp hour”), which is milli Amperes times number of hours. milli Ampere per hour in a formula would read as milli Amperes divided by number of hours, or mA/h.

In the same way as miles per hour would be miles/hour, eg. 60 miles/hour.

So battery capacity is the number of milli Amperes available to be drawn during so many hours, eg. 1000 mA for 6 hours =6000 mAh capacity.

Thanks Robert for the invaluable information that you and others bring to this forum. Very informative and wide ranging topics. I’m glad I found it on the Digikey website!

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I’m looking into corrections for this post now. Thanks very much for your support, Xmitr. We’re glad you’re finding the forums useful!