Gauge Power Calculator

Work out how much of your amplifier's power the cable throws away, and which cable to buy so it does not.

Step 1. Your amplifiers

Pick an amplifier and it is added straight away. Add as many as your system runs. Not listed? Choose Custom Amp, fill in the details and press Add Amp.

Our range comes from our own catalogue. Other brands is our best reading of each manufacturer's published specifications, and we do not sell those amps. If you have better figures for yours, use Custom Amp.

Model	Description	Channels	Type	Rated (W)	Consumed (W)	V	A	Output (W)
			Total:

Step 2. What cable you need

	2x0	0	2	4	8	10
Maxcor OFC
Maxcor
Bassix

Black = Dangerously bad.

Step 3. Your cable run

Drag the length and the advice above updates as you go. Measure the power run, battery to amp. We add the 0.8m earth lead from our kits for you.

Cable length 4.5 m

Those two only change the Consumed and Output columns in the amplifier table. The grid always shows every combination we sell.

Power cable, explained

What this calculator does, and why it matters. Skip to whichever bit you need. The maths is all here if you want to check it.

Resistivity, AWG areas and amplifier efficiency are standard engineering figures. Amplifier ratings come from each manufacturer. Cable construction figures are our own.

Add one row per amplifier. Not in the list? Pick Custom Amp and type the numbers in.

The columns

Type: the amplifier's class. Some classes waste more of the power they draw than others, so two amps with the same output can pull very different current.
Rated (W): total continuous RMS output at the amp's lowest stable impedance, or bridged. That is the hardest it can be worked, so it draws the most current. It is usually lower than the big number on the box, which is normally a peak figure.
Consumed (W): what the amp has to draw to produce that output, once its own losses are counted.
V: the supply voltage the amp was rated at. Usually 14.4V.
A: the current that works out to.
Output (W): what you actually get once the cable has taken its cut.

What to buy

The panel above the grid picks for you. For each of our three ranges it finds the thinnest cable that still does the job. Thinnest, because cable heavier than you need costs more, is harder to route, and buys you nothing.

"Does the job" means two things: the supply at the amp stays above 11V, and the cable loses no more than 5% of your power. That 5% is a 2.5% voltage drop, well inside the 3% the trade works to. Anything under 2% is marked comfortable. If no gauge in a range can manage it, we say so.

Maxcor OFC usually needs a thinner gauge than the two CCA ranges, because copper conducts better. That is what you are paying for.

The colour grid

Every cable and gauge we sell, showing the watts lost. Lower is better.

Green: 2% or less lost. Nothing to worry about.
Yellow: 2% to 5%. Fine, but there is a better option on the grid.
Red: over 5%. Go thicker or shorten the run. If the whole grid is red, the run itself is the problem.
Black: the amp is seeing under 11V. Most amps shut down or distort around there, and staying low damages them. This is checked before the percentages, so a cell can go black even when very little is being lost. On a big enough system the current alone pulls the voltage down.
Fuchsia: the maths has gone below zero volts. Something has to change.

Four steps. It is Ohm's law and a table of metals.

1How much current does the amp draw?

current (A) = rated power (W) / efficiency / supply voltage (V)

No amplifier is 100% efficient. Whatever it does not deliver leaves as heat, so an amp making 760W pulls rather more than 760W from the battery. The efficiencies we use:

Class	Efficiency	Why
D ("Digital")	80%	Real class D runs 80 to 90%. We hold it at 80 on purpose. A lower figure predicts more current, so it errs towards thicker cable.
AB	60%	Typical for class AB at full output.
A	25%	25% is the theoretical maximum for class A.

A Hertz CP 4.800 is rated 760W and is class D. 760 / 0.80 / 14.4 = 65.97A.

2How much resistance is in the cable?

resistance (Ω) = resistivity × length (m) / area (mm²)

Resistivity is a property of the metal. Length works against you, thickness works for you. Double the area and you halve the resistance. Length here is the whole loop: power run plus earth lead.

Resistivity at 20°C, in Ω·mm²/m
Conductor	Resistivity	Conductivity
Copper (OFC)	0.01724	100%
Copper-clad aluminium (CCA)	0.02710	64%
Aluminium	0.02820	61%

4 gauge is 21.2mm². A 4.5m run plus 0.8m of earth is 5.3m of CCA. 0.02710 × 5.3 / 21.2 = 0.00678Ω.

3How much voltage does that cost?

voltage drop (V) = current (A) × resistance (Ω)

Ohm's law. Voltage lost in the cable never reaches the amp. It turns into heat along the run, which is why undersized cable gets warm.

65.97 × 0.00678 = 0.45V lost. An amp on a 14.5V system sees 14.05V.

4What does the amp manage on that?

available power (W) = rated power (W) × (voltage at amp / supply voltage)²

An amplifier's output rises and falls with the square of its supply voltage. That is why voltage drop hurts more than people expect. Lose 3% of your voltage and you lose about 6% of your output.

760 × (14.05 / 14.5)² = 713.9W. The cable cost you 46.1W, or 6.1%.
The same run in 4AWG OFC drops only 0.28V and costs 29.5W (3.9%).

Current makes a round trip. It leaves the battery positive, runs down the power cable to the amp, then has to get back to the battery negative. It does that through a short earth lead to the car body, then through the body steel.

Both legs have resistance. Both lose voltage. Counting only the power cable measures half the journey, so we add the earth lead for you. All our kits include 0.8m of it in the same gauge as the power cable, so adding it is exact rather than a guess.

At 4.5m that 0.8m is another 18% of resistance. On a 12m limo run it is only 6%. The shorter the run, the more the earth lead matters.

The earth point is where installs actually fail. Chassis steel is a big lump of metal, so its own resistance is tiny and we ignore it. A bad connection to it is another story. Paint left under the terminal, surface rust, or a self-tapper into thin sheet can add more resistance than the whole cable run. Worse, it gets worse over time as it corrodes. Scrape back to bright bare metal, use a ring terminal and a bolt, then seal it.

Running the earth all the way back to the battery roughly doubles your cable length, and roughly doubles the loss. Earth locally, and earth it properly.

Electrically, a gauge number tells you one thing: how much metal is in the cable. Strand count, jacket, colour and how bendy it feels all change handling, not resistance.

AWG numbers run backwards. Smaller number, thicker cable. Each step up adds about 26% more metal, so three steps doubles it. 1 gauge has twice the metal of 4 gauge (42.4mm² against 21.2mm²), and half the resistance.

American Wire Gauge, nominal conductor area
AWG	Area (mm²)	AWG	Area (mm²)
4/0 (0000)	107.2	2	33.6
3/0 (000)	85.0	4	21.2
2/0 (00)	67.4	6	13.3
1/0 (0)	53.5	8	8.37
1	42.4	10	5.26

"00" here is not 2/0 cable. It means two separate runs of 0 gauge. Between them they have about the same metal as 4/0, around 107mm². The maths lands in the same place, but they are not the same product.

AWG rated or GA rated?

AWG is a standard with defined sizes. GA is not. It is a label, and a cable sold as 8GA does not have to contain the 8.37mm² that real 8 AWG needs. This is the most common way of comparing two cables and getting it wrong.

Our own two CCA ranges, both sold at 8 gauge:

Each 0.12mm strand is 0.01131mm²
Cable	Strands	Actual metal	Against real 8 AWG
Maxcor	735	8.31mm²	99%, genuinely 8 AWG
Bassix	616	6.97mm²	83%, nearer 8.8 AWG

Bassix is labelled honestly. It is GA rated, not AWG rated, and its power ratings match what it really carries. But at the same stated gauge it holds about 17% less metal than Maxcor, which shows up as roughly 20% more loss in the grid. That is the difference you are paying for, and why they sit on separate rows.

OFC, oxygen-free copper

Solid copper with the oxygen refined out, so it does not go brittle or corrode from the inside. It is the benchmark: 100% conductivity. Tinned OFC coats every strand in tin, which resists corrosion in damp, salty and marine installs.

CCA, copper-clad aluminium

An aluminium core with a copper skin bonded to it. You get copper's terminals and solderability at aluminium's weight and price. It conducts about 64% as well as copper.

What that means on the tools:

Resistance: same size for size, CCA resists about 1.6 times as much as copper. To match a copper cable you need about 1.6 times the metal, which is two AWG sizes up. A 4GA CCA behaves like a 6 AWG copper.
Weight and cost: about a third the weight, and noticeably cheaper. That is why CCA exists, and on a long boot run the weight saving is real.
Terminals: aluminium oxidises, and the oxide does not conduct. Crimps have to be properly gas-tight. A lazy termination on CCA builds resistance and then heat, where copper would forgive you.
Flexing: CCA is stiffer and hardens as it works, so it likes being moved less. Support it where it goes through the bulkhead.

Neither is "better". A correctly sized CCA cable with a good earth beats an undersized OFC one with a painted earth point. Material matters less than thickness, and thickness matters less than your two end connections.

It answers one question: how much power the cable costs you. It is not a whole install plan.

Fusing. This works out voltage drop, not how much current a cable can safely carry. Fuse to protect the cable, at the battery end, and follow the rating on your kit.
Heat. Every figure here is at 20°C. Copper gains about 0.4% resistance per degree, so a run through a hot engine bay at 60°C resists about 16% more than we show.
Real music. We assume every amp is at full rated output, continuously, all at once. That is the true worst case, and music never does it. Against the maximum consumption manufacturers publish for their own amps, we come out about 1.9 times higher. That is deliberate. We would rather you went home with cable that is too thick than too thin. If our numbers look big next to the fuse on your amp, that is why.
Your charging system. Alternator, battery and the factory earth straps all sit upstream of anything here. A tired alternator undoes a perfect cable run.
Speaker cable. Same physics between amp and speaker, but we do not model it.

AWG: American Wire Gauge, a standard with defined sizes. Lower number, thicker cable. Three steps doubles the metal.
GA: A size label, not a standard. A cable sold as 8GA need not hold as much metal as real 8 AWG. Check the strand count.
CCA: Copper-clad aluminium. Aluminium core, copper skin. About 64% as conductive as copper and about a third the weight.
OFC: Oxygen-free copper, the 100% benchmark. Tinned OFC adds corrosion resistance for marine and damp installs.
RMS: The power an amp can hold continuously, as opposed to peak or "max" figures it can only touch briefly.
Class A, AB, D: Amplifier designs with different efficiencies: roughly 25%, 60% and 80 to 90%. The less efficient the amp, the more current it pulls for the same output.
Resistivity: How strongly a metal resists current, whatever shape it is in.
Voltage drop: Voltage lost along the cable instead of reaching the amp. It leaves as heat.
Bridging: Joining two amp channels to drive one speaker harder. It pulls more current, which is why we use bridged ratings where they apply.
Impedance: The load a speaker puts on the amp, in ohms. Lower impedance pulls more power and more current, so ratings are always quoted against it.

More on wire gauge standards: American Wire Gauge (Wikipedia).