WireSizer

WireSizer is the simple and intuitive way to calculate the wire gauge needed for a desired voltage drop for most common DC applications up to 60 volts. It is great for doing quick calculations when updating wiring on boats, RVs, trucks, cars, radios, or other "low voltage" DC applications for both do-it-yourselfers and professionals.
Others agree!
"This app is a joy to use! ...you'll be able to get the right wire gauge to use every time. Nice." - Cruising World Blog (11/27/2012)
"It is a must have for your electrical toolbox." - i-marineapps (2/9/2013)
To find your proper wire, simply select your DC voltage, your current, and the length of your circuit with simple flicks of your finger. No keyboard input needed! WireSizer will automatically calculate the minimum wire size for different percentages of voltage drop under normal or "engine compartment" operating conditions using copper wire. Wire gauge recommendations include commonly available sizes in AWG, SAE and ISO/Metric.
Using properly sized wire is important. Undersized wire can lead to equipment malfunction or failure, and oversized wire will add to cost and can be harder to work with. And unlike "online" wire gauge calculators, WireSizer will work wherever or whenever you need it.
WireSizer allows you to select voltages up to 60 VDC, current up to 500 amps, and total circuit length in feet or meters up to 600 feet (or 200 meters).
Results calculated are for voltage drops between 1 and 20 percent (which you can "flip" through to find the one which is best for your purpose), and wire sizes between 4/0 and 18 gauge AWG and SAE, and 0.75 to 92 mm.
WireSizer will also let you select whether the wire is going to run through an engine compartment or a similarly "hot" environment, is sheathed, bundled, or in conduit, and select the wires insulation rating (60C, 75C, 80C, 90C, 105C, 125C, 200C) to fine tune your results.
And finally, the voltage drop calculation results are compared with the safe current carrying capacity (or "ampacity") of the wire, to make sure the wire suggested is suitable.
And for your convenience, WireSizer also includes a "Materials List" for you to record all of your wire selections.
WireSizer gauge calculation results meet ABYC E11 specifications (standard requirement for boats, excellent guidelines for other uses) provided you have clean connections, and are using good quality wire. ABYC specifications meet or exceed NEC where applicable, and correspond to ISO/FDIS.
* * * NOT FOR USE WITH AC CIRCUITS * * *
If you have any questions (or complaints!), please email us.
Ad free, and will cost less than the wire scraps you probably throw away at the end of the day.