What Size Generator Do I Need for My Job Site or Home Project?
By the team at Beehive Rental & Sales — Serving Southern Utah's contractors and homeowners since 1994.
Choosing the wrong size generator wastes money — too small and it overloads, too large and you are paying for capacity you do not use. Getting the right match between your power needs and generator output is simpler than most people think, and it comes down to basic math: add up your running watts, account for starting surges, and select a generator with adequate capacity and a safety margin.
“Quick Answer: To determine what size generator you need, add the running wattage of all tools and devices you will use simultaneously, then add a 25% safety margin. Most residential job sites need a 5,000-8,000 watt generator; full construction sites typically require 10,000-15,000 watts. BeeHive Rental & Sales carries portable through towable generators — call (435) 628-6663 for sizing help.
Key Takeaways
- •Add running watts first, then account for starting watts — Electric motors draw 2-3x their running wattage on startup, so size your generator for the highest starting surge plus the running load of everything else
- •Most single-trade job sites need 5,000-8,000 watts — This covers a circular saw, air compressor, lights, and a charger running simultaneously
- •Welding requires a dedicated or large generator — Welders draw 8,000+ starting watts; either rent a welder/generator combo or a 12,000W+ generator
- •Remote Southern Utah job sites in Toquerville, Leeds, Virgin, and Kolob often have no grid power, making proper generator sizing critical
- •Browse generators available for rent at BeeHive Rental & Sales in St. George
Generator Sizing: The Simple Method
The process is straightforward. Follow these three steps and you will select the right generator every time.
Step 1: List Every Tool and Device You Will Run
Write down every piece of equipment, tool, light, and device that might run at the same time. Be realistic — you probably will not run every tool simultaneously, but account for the tools that overlap.
Step 2: Add Up Running Wattage
Every electrical tool has a running wattage (also called rated watts). Add these up for everything running at the same time.
Step 3: Account for Starting Watts
Electric motors require 2-3 times their running wattage to start. Identify the tool with the highest starting wattage. Your generator must handle: total running watts of all tools + starting watts of the largest tool.
The Formula
Required generator size = (Sum of all running watts) + (Highest single starting watt demand) + 25% safety margin
The 25% margin accounts for altitude (generators lose about 3% capacity per 1,000 feet of elevation — relevant for Southern Utah sites above 3,000 feet), temperature effects (hot Southern Utah summers reduce output slightly), and the general principle that running a generator at sustained full load shortens its life.
Common Tool Wattage Reference Table
Use this table to calculate your power requirements. Running watts are what the tool uses during normal operation. Starting watts are the momentary surge when the motor kicks on.
Power Tools
| Tool | Running Watts | Starting Watts |
|---|---|---|
| Circular saw (7-1/4") | 1,400 | 2,300 |
| Miter saw (12") | 1,800 | 2,500 |
| Table saw (10") | 1,800 | 4,500 |
| Reciprocating saw | 1,200 | 1,500 |
| Angle grinder (4-1/2") | 900 | 1,400 |
| Drill (1/2" hammer drill) | 600 | 900 |
| Impact driver | 300 | 300 |
| Router | 1,400 | 2,000 |
| Jigsaw | 500 | 700 |
| Belt sander | 1,200 | 1,800 |
| Planer (portable) | 1,800 | 2,400 |
Construction Equipment
| Equipment | Running Watts | Starting Watts |
|---|---|---|
| Air compressor (1-1/2 HP) | 1,600 | 4,000 |
| Air compressor (5 HP) | 2,400 | 6,000 |
| Concrete vibrator | 1,000 | 1,800 |
| Concrete mixer (1/2 bag) | 600 | 1,800 |
| Concrete mixer (1 bag) | 1,000 | 3,000 |
| Demolition hammer (electric) | 1,200 | 1,500 |
| Welder (MIG, 180-amp) | 5,000 | 8,000 |
| Welder (stick, 225-amp) | 6,000 | 9,000 |
| Plasma cutter | 4,000 | 6,500 |
Lighting and Support
| Item | Running Watts | Starting Watts |
|---|---|---|
| Work light (500W halogen) | 500 | 500 |
| LED light tower | 200 | 200 |
| String lights (100 ft LED) | 100 | 100 |
| Battery charger (tool batteries) | 200 | 200 |
| Job site radio | 50 | 50 |
| Space heater (electric) | 1,500 | 1,500 |
| Fan (box fan) | 200 | 350 |
| Portable A/C unit | 1,300 | 2,600 |
Pumps
| Pump Type | Running Watts | Starting Watts |
|---|---|---|
| Sump pump (1/3 HP) | 800 | 1,300 |
| Sump pump (1/2 HP) | 1,050 | 2,150 |
| Trash pump (2") | 1,100 | 2,500 |
| Submersible pump (1 HP) | 1,500 | 3,000 |
Generator Size Categories
Based on the wattage calculations, here is where most projects fall.
Portable: 2,000-4,000 Watts
Best for: Single-tool operation, charging batteries, lighting a small work area, basic home projects.
Typical setup: One power tool at a time plus lights and a charger.
Example load:
- •Circular saw (1,400W running)
- •LED work lights (200W)
- •Battery charger (200W)
- •Total running: 1,800W | Peak with saw start: 2,700W
A 3,500W generator handles this with room to spare.
Pros: Lightweight, easy to transport, fuel-efficient, quiet Cons: Cannot run multiple large tools simultaneously
Medium: 5,000-8,000 Watts
Best for: Most residential job sites, single-trade crews, home renovation projects.
Typical setup: Two to three tools running simultaneously, plus lights and support equipment.
Example load:
- •Air compressor, 1.5 HP (1,600W running)
- •Circular saw (1,400W running)
- •LED lights (400W)
- •Charger and radio (250W)
- •Total running: 3,650W | Peak with compressor start: 6,050W
A 7,500W generator handles this reliably.
Pros: Covers most construction scenarios, still portable (with wheels), reasonable fuel consumption Cons: Heavy (150-250 lbs), louder than small units
Large: 10,000-15,000 Watts
Best for: Full construction sites, multi-tool operations, crews with welding needs.
Typical setup: Multiple tools, compressor, welder or large power draws, full lighting.
Example load:
- •Air compressor, 5 HP (2,400W running)
- •Miter saw (1,800W running)
- •Angle grinder (900W running)
- •Concrete vibrator (1,000W running)
- •Lights and support (600W)
- •Total running: 6,700W | Peak with compressor start: 10,300W
A 12,000W generator provides this with adequate margin.
Pros: Runs nearly any combination of standard construction tools, can handle welders Cons: Heavy (300-500 lbs), requires a truck or trailer to move, higher fuel consumption
Towable: 20,000+ Watts
Best for: Commercial construction, multi-trade sites, temporary power for events or buildings under construction.
Typical setup: Full site power including welders, compressors, lighting arrays, and temporary building power.
Pros: Essentially a portable power plant, can power multiple circuits, diesel-powered for long runtime Cons: Requires towing vehicle and setup, higher rental cost, requires fuel planning
BeeHive Rental & Sales carries generators in all four categories. The team can help match your specific tool list to the right unit — call (435) 628-6663 or stop by 1175 Highland Drive.
Fuel Type Comparison
Gasoline Generators
Pros: Lower purchase/rental cost, widely available fuel, easy to start in warm weather. Cons: Shorter runtime per tank, fuel degrades over time, slightly lower efficiency. Best for: Short-duration projects, homeowner use, portable applications.
Diesel Generators
Pros: Superior fuel efficiency (30-50% better than gas), longer engine life, safer fuel storage (less volatile), better for sustained heavy loads. Cons: Higher upfront cost, louder operation, harder cold starts (not an issue in Southern Utah summers). Best for: Commercial job sites, multi-day projects, towable units.
Dual Fuel (Gas/Propane)
Pros: Fuel flexibility, propane runs cleaner and stores indefinitely, switch fuel types without stopping. Cons: Slightly lower output on propane (about 10% less), more complex fuel systems. Best for: Extended projects, backup power, operators who want fuel flexibility.
Runtime Calculations
Knowing how long your generator runs on a tank helps you plan fuel purchases and avoid mid-day shutdowns.
Estimating Runtime
Runtime (hours) = Fuel tank capacity (gallons) / Fuel consumption rate (gallons per hour)
Fuel consumption depends on load. Most generators at 50% load consume roughly:
| Generator Size | Fuel Type | Consumption at 50% Load | Typical Tank Size | Runtime at 50% |
|---|---|---|---|---|
| 3,500W | Gas | 0.5 gal/hr | 4 gallons | 8 hours |
| 7,500W | Gas | 0.8 gal/hr | 8 gallons | 10 hours |
| 12,000W | Gas | 1.2 gal/hr | 12 gallons | 10 hours |
| 12,000W | Diesel | 0.8 gal/hr | 12 gallons | 15 hours |
| 20,000W+ | Diesel | 1.5 gal/hr | 30+ gallons | 20+ hours |
Tip: Running a generator at 50-75% capacity is the sweet spot for fuel efficiency and engine longevity. This is another reason proper sizing matters — an oversized generator at 25% load wastes fuel, and an undersized generator at 100% load burns fuel fast and wears out quickly.
Noise Considerations for Residential Areas
St. George, Washington, Hurricane, and Ivins all have noise ordinances that affect construction sites. Generators are a common source of neighbor complaints.
Noise Levels by Generator Type
| Type | Typical Noise Level | Equivalent Sound |
|---|---|---|
| Inverter (2,000-4,000W) | 50-60 dB | Normal conversation |
| Conventional portable (5,000-8,000W) | 65-75 dB | Vacuum cleaner |
| Large portable (10,000-15,000W) | 72-80 dB | Lawn mower |
| Towable diesel (20,000W+) | 70-85 dB | Heavy traffic |
Inverter generators are specifically designed for quiet operation and produce cleaner power (important for sensitive electronics). They cost more to rent but are worth it for residential work.
Noise Reduction Tips
- •Position the generator as far from neighbors as practical — every doubling of distance reduces perceived volume significantly
- •Point the exhaust away from occupied areas
- •Place the generator behind your work vehicle or structure to create a sound barrier
- •Start early in the day rather than running late — most noise ordinances restrict hours, typically no construction noise before 7 AM or after 8 PM
Southern Utah Generator Considerations
Remote Job Sites
Many Southern Utah construction and improvement projects are located far from grid power. Properties in Toquerville, Leeds, Virgin, Rockville, Apple Valley, and the Kolob area may have no electrical service at all during the building phase.
For remote sites:
- •Bring a larger generator than you think you need — you cannot plug in an extension cord if you run short
- •Carry extra fuel — the nearest gas station may be 20+ miles away
- •Consider a dual-fuel model for fuel flexibility
- •A towable diesel generator provides the most reliable power for multi-day or multi-week remote site work
Altitude Effects
Southern Utah job sites range from 2,600 feet (St. George valley) to over 7,000 feet (Pine Valley, Kolob). Gasoline generators lose approximately 3-3.5% of their rated output per 1,000 feet above sea level.
| Elevation | Output Loss | 7,500W Generator Actual Output |
|---|---|---|
| 2,600 ft (St. George) | ~8% | ~6,900W |
| 4,000 ft (Hurricane/Diamond Valley) | ~12% | ~6,600W |
| 5,500 ft (Leeds/Veyo) | ~17% | ~6,225W |
| 7,000 ft (Pine Valley) | ~21% | ~5,925W |
Account for altitude loss when sizing your generator for higher-elevation projects. Diesel generators are less affected by altitude than gasoline models.
Heat Effects
Southern Utah summers regularly exceed 105 degrees Fahrenheit. High ambient temperatures reduce generator cooling efficiency and can cause thermal shutdown.
- •Keep generators in shade when possible
- •Ensure adequate airflow — do not enclose a generator
- •Monitor temperature gauges during extended operation in extreme heat
- •Allow cool-down periods during the hottest part of the day if running near capacity
Generator Safety
Carbon Monoxide Hazard
Generators produce carbon monoxide, which is odorless and lethal. Never operate a generator inside a building, garage, enclosed trailer, or any partially enclosed space. Position generators at least 20 feet from doors, windows, and air intakes with the exhaust pointing away from occupied areas.
Grounding
Job site generators must be properly grounded. Drive a ground rod at least 4 feet into the soil and connect it to the generator's grounding terminal with appropriate gauge wire. In Southern Utah's rocky soil, you may need a longer ground rod or a grounding plate.
Fuel Safety
- •Never refuel a running or hot generator — shut it down and wait 5 minutes for cooling
- •Store fuel in approved containers away from the generator and heat sources
- •Keep a fire extinguisher rated for flammable liquids within reach
Electrical Safety
- •Use heavy-duty, outdoor-rated extension cords sized for the load
- •Never backfeed a generator into a building's electrical panel without a transfer switch
- •Protect connections from moisture, especially during monsoon season thunderstorms
- •Use GFCI protection for all outdoor circuits
FAQ
What size generator do I need to run a welder on a job site?
A 180-amp MIG welder needs approximately 8,000 starting watts. To run a welder plus basic tools and lights, you need a minimum 10,000-watt generator, and a 12,000-watt model is more comfortable. Alternatively, consider a welder/generator combination unit, which integrates both functions into one machine. BeeHive Rental & Sales carries both standalone generators and welder/generator combos for job site use.
Can I run two air compressors on one generator?
It depends on the compressor sizes and the generator. Two 1.5 HP compressors each draw about 4,000 starting watts, and if they start simultaneously, you need 8,000+ watts available. The safest approach is to start one compressor, let it reach full pressure, then start the second. A 10,000W generator handles two small compressors comfortably with staggered starts. Always size for the worst case.
What is the difference between running watts and starting watts?
Running watts (rated watts) are the continuous power a tool uses during normal operation. Starting watts (surge watts) are the brief spike of power needed to start an electric motor — typically 2-3 times the running wattage. This surge lasts only 1-3 seconds. Your generator must handle the highest starting surge plus the running watts of everything else operating simultaneously.
How do I know if my generator is overloaded?
Signs of generator overload include dimming lights, tools running slower than normal, the generator bogging down or surging, circuit breakers tripping on the generator panel, and visible exhaust smoke. Persistent overloading damages both the generator and your connected tools. If you see these signs, disconnect non-essential loads immediately and reassess your power needs.
Is it better to rent a generator or buy one?
For occasional use (a few projects per year), renting is significantly more economical. A quality 7,500W generator costs $1,500-$3,000 to purchase, plus annual maintenance. Renting the same generator for a weekend costs a fraction of that, includes maintenance, and gives you access to the right size for each specific project. Buy only if you need a generator on-site more than 80+ days per year. BeeHive Rental & Sales offers daily, weekly, and monthly generator rental rates.
Need help choosing the right generator for your project? BeeHive Rental & Sales has been powering Southern Utah job sites since 1994. The team will help you calculate your load requirements and select the right generator — no more guessing. Call (435) 628-6663, visit 1175 Highland Drive in St. George, or browse available generators online.