Introduction
The Lighting Power Calculator totals up the wattage of all your lighting fixtures and converts that to amperage draw at your available circuit voltage. You add each light with its wattage, and the tool shows your total power consumption plus the number of standard 15-amp or 20-amp circuits you need. This prevents the most common electrical problem on film sets: tripping breakers by overloading a circuit, which kills all your lights mid-take and can damage equipment.
What This Tool Calculates
Every practical location has a limited electrical capacity. A standard residential outlet in the United States provides 15 or 20 amps at 120 volts, which means 1,800 to 2,400 watts per circuit. A single 2K tungsten fresnel draws 2,000 watts and will trip a 15-amp breaker by itself. Even LED lighting, which is far more efficient than tungsten, adds up quickly when you are running multiple fixtures plus hair lights, practicals, and background lights. Tripping a breaker is not just an inconvenience. It interrupts takes, can corrupt digital recordings, and wastes everyone's time while the gaffer traces the circuit and rebalances the load. On locations with limited power, exceeding the building's total capacity can require bringing in a generator, which adds significant cost.
The Formula and How It Works
Amperage equals watts divided by voltage. A 1,000 W light on a 120 V circuit draws 1000 / 120 = 8.33 amps. The tool sums all fixture wattages, divides by your voltage (120V or 240V), and shows total amperage. It then divides total amperage by the circuit rating (15A or 20A) to tell you how many circuits you need. The standard safety rule is to load circuits to no more than 80 percent of capacity, so a 20-amp circuit should carry no more than 16 amps. The calculator applies this derating automatically.
Real-World Examples
How to Use This Calculator
Add each lighting fixture by name and wattage. Select your circuit voltage (120V for standard US outlets, 240V for European or industrial circuits). Select your circuit breaker rating (typically 15A or 20A for residential, 30A or 50A for industrial). The calculator shows total wattage, total amperage, and the minimum number of circuits required to safely distribute the load. Use this before arriving at a location to determine whether you need additional power distribution or a generator.
Tips from Working Professionals
| Detail | Value |
|---|---|
| Experienced gaffers recommend mapping the circuit breakers at every practical location during the tech scout. | |
| Know which outlets are on which breakers before you start plugging in lights. | |
| Never assume that two outlets in the same room are on the same circuit, and never assume they are on different circuits. | |
| Use a circuit tester to verify. | |
| When using dimmer boards, remember that the dimmer itself consumes additional power, so factor in a 5 to 10 percent overhead for dimming equipment.. |
Pro Tips and Common Mistakes
Pro Tips
- Gaffers and best boys use this tool for every location shoot where they are drawing from house power rather than a generator.
- Production managers use it to assess whether locations can support the lighting plan or whether generator rental needs to be added to the budget.
- Independent filmmakers working without a dedicated electrical department need this calculation to avoid damaging locations and tripping breakers..
Common Mistakes
- What if I am using LED lights? LED lights have much lower wattage for equivalent output.
- A 200W LED panel might replace a 1,000W tungsten light.
- Enter the actual LED wattage, not the tungsten-equivalent rating.
Frequently Asked Questions
Can I mix 120V and 240V fixtures?
Yes, but they must be on separate circuits at the appropriate voltage. Never plug a 120V fixture into a 240V outlet or vice versa.
What is the 80 percent rule?
The National Electrical Code recommends loading circuits to no more than 80 percent of their rated capacity for continuous loads (more than 3 hours). Film sets are continuous loads.
Start Calculating
Gaffers often do this math on paper or in their heads, which works until the numbers get complex. This tool gives you an instant, accurate answer with the 80 percent safety derating applied automatically. It is free, runs in your browser, and is designed specifically for the on-set electrical planning that film crews need.
