Sub Box Calculator › Amp wiring calculator
Amp wiring calculator
Enter your amp’s RMS power, your subs, where the amp goes and what radio you have. You get the power and ground wire gauge, the fuse size at the battery, how to get the signal and turn-on, a wiring diagram and a shopping list with lengths.
How the wire gauge is chosen
Two conditions, and the thicker result wins:
- Heat. The wire must safely carry the current of the fuse that protects it. We use the ABYC E-11 table for 105 °C wire with the correction for the engine bay, because the power wire runs through it.
- Voltage drop. At full power the drop on the power and ground wires together should stay within 0.5 V. The longer the run, the thicker the wire.
The current comes from the amp’s RMS power: class D amps turn about 80 % of the battery power into sound, class AB about 55 %. A 1000 W RMS class D amp draws about 91 A at 13.8 V. If you know the amp’s own fuse rating, enter it: it is the most accurate guide.
Where the fuse goes and how big it is
The main fuse goes at the battery, no more than 18″ (45 cm) from the terminal. It protects the wire: if the wire shorts to the body anywhere along the way, the fuse blows before the wire catches fire. That is why its rating follows the wire, not the amp. A 4 AWG wire with a 200 A fuse is a common and dangerous mistake.
Copper vs CCA
Copper-clad aluminum (CCA) is cheaper and is in most budget kits. It has about 60 % of the conductivity of copper, so a CCA wire must be one or two sizes thicker. Many “4 gauge” kits are also thinner than real 4 AWG (21 mm²). The ANSI/CTA-2015 standard sets the real size of each car audio gauge: look for cable marked as compliant, or buy by mm².
Wiring an amp to a factory radio
A factory radio has no RCA outputs. Most amps have a speaker-level (high-level) input: connect it to the rear speaker wires, and many amps then turn on by themselves when a signal appears. Otherwise use a line output converter (LOC). Premium factory systems often cut the bass at high volume; there you need an active converter with bass restoration.
Car audio wire gauge chart
Copper (OFC) power wire for a class D amp, 2 ft (0.6 m) ground. The fuse is the same for every length. For CCA go one or two sizes thicker.
| Amp RMS | 10 ft · 3 m | 13 ft · 4 m | 18 ft · 5.5 m | 23 ft · 7 m | Fuse |
|---|---|---|---|---|---|
| 300 W | 10 AWG · 6 mm² | 10 AWG · 6 mm² | 8 AWG · 6 mm² | 8 AWG · 10 mm² | 40 A |
| 500 W | 8 AWG · 10 mm² | 8 AWG · 10 mm² | 4 AWG · 10 mm² | 4 AWG · 16 mm² | 60 A |
| 800 W | 4 AWG · 16 mm² | 4 AWG · 16 mm² | 4 AWG · 16 mm² | 4 AWG · 20 mm² | 100 A |
| 1,000 W | 4 AWG · 20 mm² | 4 AWG · 20 mm² | 4 AWG · 20 mm² | 2 AWG · 25 mm² | 125 A |
| 1,500 W | 2 AWG · 35 mm² | 2 AWG · 35 mm² | 2 AWG · 35 mm² | 1/0 AWG · 50 mm² | 175 A |
| 2,000 W | 2/0 AWG · 70 mm² | 2/0 AWG · 70 mm² | 2/0 AWG · 70 mm² | 2/0 AWG · 70 mm² | 250 A |
FAQ
What gauge wire do I need for a 1000 watt amp?
For a class D amp with up to about 18 ft (5.5 m) of power wire: 4 AWG copper (OFC) and a 125 A fuse at the battery. With CCA wire: 2 AWG. A class AB amp of the same power draws more current and needs thicker wire.
Where should the amp fuse be?
At the battery, within 18 inches (45 cm) of the positive terminal. If the amp has no fuses of its own, add a second one within 18 inches of the amp.
Should the ground wire be the same gauge as the power wire?
Yes. The same current flows through both. Keep the ground short and bolt it to bare metal of the body, with the paint sanded off.
Do I need a capacitor for my amp?
Usually not. A 1 farad capacitor supplies 90 A for only about 5 milliseconds. If your lights dim, the fix is the Big 3 upgrade, a good AGM battery and, for big systems, a high-output alternator.
When do I need the Big 3 upgrade?
From about 1500 W RMS, or earlier if your lights dim on bass. It replaces the three factory cables between the alternator, battery, body and engine with thicker ones.