Beginner
SoundBox
SoundBox PCK0 1/0 kit
$39.95A complete 1/0 kit at the lowest price here, which is the right call when the budget is going into the amplifier.
Check price on AmazonElectrical calculator
Amplifier Wire Gauge and Voltage Drop Calculator
Quick answer
Voltage drop is twice the one-way run length times the current times the resistance per foot. An 87 amp draw over a 17 foot run needs 1/0 gauge to stay under 2 percent drop, and the doubling is the return path through the chassis.
Result
Minimum wire size 2/0 AWG Published figure
Current draw 86.8 A Convention
Voltage drop 0.285 V Published figure
Drop as a percentage 1.98 %
Ground the amplifier to bare chassis metal with the same gauge as the power wire and the shortest run you can manage. A long, thin ground undoes an expensive power wire completely.
The formula
Vdrop = 2 x run length x amps x (ohms per 1000 ft / 1000)
The 2 is the return conductor. Current leaves through the power wire and comes back through the ground path, and it drops voltage in both. Forgetting it halves the calculated drop and undersizes the cable by a full step or more, which is the most common wiring error in car audio.
The figures above are computed with these exact inputs: Amplifier RMS power 1000 W, Run length, one way 17 ft, Maximum voltage drop 2 %, Amplifier class d.
What this calculator assumes
Some of these are published physics or manufacturer figures and some are conventions. They are not the same kind of number, so each one is labeled.
| Assumption | Kind | Where it comes from |
|---|---|---|
| NEC Chapter 9 | Published figure | NEC Chapter 9, Table 8, uncoated stranded copper at 75 C |
| NEC Table 310.16 | Published figure | NEC Table 310.16, 75 C copper |
| Class D Efficiency: 0.8 | Convention | A planning efficiency for a class D mobile amplifier at typical listening levels. Real efficiency varies with load impedance, output level and the amplifier itself, and no standards body publishes a single figure |
Gear that matches this result
Every card below is in the page source. The calculator re-ranks them against your numbers and marks anything that falls short of what you just calculated.
Beginner
ORION
Orion Cobalt COKIT0
$49.95States true American Wire Gauge rather than an inflated "0 gauge" marking, which is the thing to check on a cheap kit.
Check price on Amazon Intermediate
CT Sounds
CT Sounds 1/0 CCA kit
$54.99Copper clad aluminum, which is fine at this gauge for most systems and much cheaper than copper.
Check price on Amazon Intermediate
Gravity
Gravity PK2 0 gauge kit
$58.99Includes an ANL holder with both 250 and 300 amp fuses, so the fuse can match the wire rather than the box contents.
Check price on Amazon Expert
AUDIO360
Audio360 AD0C true spec
$64.99True spec 0 AWG with a 17 foot run and two fuse values, which is the kit to buy when the wire itself matters.
Check price on Amazon Expert
RECOIL
Recoil RCK0D dual amplifier kit
$76.99Sized for two amplifiers from one run, which is cheaper and tidier than two separate runs from the battery.
Check price on AmazonFrequently asked questions
- How does the wire gauge calculation work?
- Vdrop = 2 x run length x amps x (ohms per 1000 ft / 1000). The 2 is the return conductor. Current leaves through the power wire and comes back through the ground path, and it drops voltage in both. Forgetting it halves the calculated drop and undersizes the cable by a full step or more, which is the most common wiring error in car audio.
- Are these figures published or are they rules of thumb?
- Both, and the page labels which is which. The Helmholtz port relation, the Thiele/Small alignment equations, cone area geometry, Ohm’s law, conductor resistance and ampacity, and manufacturer specifications are published and are labeled as such. Amplifier efficiency, cabin gain, the farad per thousand watts rule, port area per cubic foot and coverage percentages are conventions with no measurement behind them, and they are labeled as conventions.
- Why does this calculator sometimes refuse to give an answer?
- Because there genuinely is not one. A port can be too large in area for the box and tuning asked of it, a vented alignment stops describing a useful box outside a Qts range, and a sealed box cannot produce a total Q below the driver’s own. In each case the calculator returns nothing and explains why, rather than extrapolating past the end of a published relation.
- Do I still need an installer if I use this?
- Many owners do their own 12V work, and these are the figures that work is sized from. What matters is that a car battery delivers hundreds of amps into a short without hesitating, so the main fuse goes within 18 inches of the battery positive terminal and the battery comes off before power wire goes in. If any of that is beyond what you want to take on, a professional installer is money well spent.
Researched guidance, not professional advice. These results are planning figures from published relations and manufacturer specifications. Fit the main fuse within 18 inches of the battery positive terminal, because that fuse protects the wire and the wire is what starts a fire. Disconnect the battery before running power wire, use a grommet through every piece of sheet metal, and remember that sustained high sound pressure causes permanent hearing damage.