Generator Sizing & Cost:
The Complete 2025
Homeowner’s Guide
How big a generator do you actually need — and what will the full installation really cost? Real numbers, real data, no fluff.
How to Size a Home Generator
Generator size is measured in kilowatts (kW) for standby generators, or watts (W) for portable generators. Getting the size right matters enormously — too small and you can’t run everything you need during an outage; too large and you’ve wasted thousands of dollars on capacity you’ll never use.
There are two approaches: the square footage rule of thumb (fast but approximate) and a proper load calculation (accurate, requires knowing your appliance wattages). For a permanent installation costing $8,000–$12,000, always do a proper load calculation — a good installer will do one free during their site visit.
The Square Footage Rule of Thumb
This gets you in the right ballpark quickly:
- Up to 1,500 sq ft: 10–13 kW
- 1,500–2,500 sq ft: 16–18 kW (most common)
- 2,500–3,500 sq ft: 20–22 kW
- 3,500+ sq ft: 24 kW and up
These assume your home has central air conditioning. AC is by far the largest load in most homes. If you don’t have central AC, you can often drop one size tier.
Why AC Changes Everything
A 3-ton central AC unit (common in a 2,000 sq ft home) has a starting surge of about 7,000–10,000 watts. A 5-ton unit in a larger home can surge to 15,000+ watts at startup. Your generator must handle this surge — not just the running load — or it will trip every time the AC kicks on. This single factor is why most homeowners end up sizing up from their initial estimate.
Always Build In Headroom
Whatever your load calculation shows, add 20–25% on top. Generators run more efficiently and last longer when they’re not constantly near their rated capacity. The price difference between sizing tiers is usually only $500–$1,000 on the unit — cheap insurance for years of reliable operation.
Generator Size by Home Size
Use this table as your starting point before getting a professional load calculation.
| Size | Home Size | AC Capacity | What It Powers | Installed Cost |
|---|---|---|---|---|
| 10 kW | Up to 1,200 sq ft | Up to 2-ton | Fridge, lights, outlets, small AC | $4,500–$6,500 |
| 13 kW | Up to 1,500 sq ft | Up to 2.5-ton | + Well pump, sump pump | $5,500–$7,500 |
| 16 kW Popular | 1,500–2,000 sq ft | Up to 3-ton | Full home essentials + AC | $6,500–$9,000 |
| 18–20 kW Popular | 2,000–2,500 sq ft | Up to 4-ton | Full whole-home coverage | $7,500–$10,500 |
| 22 kW | 2,500–3,500 sq ft | Up to 5-ton | Large home, all appliances | $9,000–$12,500 |
| 24–26 kW | 3,500+ sq ft | 5-ton + extra zones | Large home + hot tub, EV charging | $11,000–$16,000 |
Load Calculator: What Size Do You Need?
Check everything you want to run at the same time during an outage. We’ll estimate your minimum generator size.
Full Cost Breakdown: What Goes Into That Price
The generator unit is just one component. Here’s every cost in a complete standby generator installation.
| Generator Size | Unit Cost | Typical Installation | Total Installed | Notes |
|---|---|---|---|---|
| 10 kW | $2,500–$3,500 | $2,000–$3,000 | $4,500–$6,500 | Entry-level whole-home |
| 13 kW | $3,000–$4,000 | $2,000–$3,000 | $5,000–$7,000 | Smaller homes |
| 16–18 kW | $3,500–$5,000 | $2,500–$3,500 | $6,000–$8,500 | Most common purchase |
| 20–22 kW | $4,500–$6,000 | $2,500–$4,000 | $7,000–$10,000 | Larger homes |
| 24–26 kW | $6,000–$8,000 | $3,000–$5,000 | $9,000–$13,000 | Premium large-home |
What Homeowners Paid by Region
Labor rates vary significantly by market. These are real ranges for a 16–20kW installation with standard installation complexity.
Sizing & Cost FAQ
Always add 20–25% headroom above your calculated load. Generators run more efficiently and last longer when they’re not near capacity. The price difference between sizing tiers is usually $500–$1,000 — cheap insurance for years of reliable operation.
Probably, unless you have unusual electrical demand. A 16–18kW unit handles most 2,000 sq ft homes with central AC comfortably. Get a professional load calculation — it takes 30 minutes and will tell you exactly what you need. A good installer will do this for free during their quote visit.
Typically $2,000–$4,500 for a standard residential installation. This covers labor, transfer switch, concrete pad, gas line hookup, and permits. Installation is often 40–60% of the total project cost. Always get an all-in quote — some installers advertise low unit prices and make it up in installation charges.
Generally no — conventional gas standby generators don’t qualify for federal tax credits. However, some states offer rebates particularly in hurricane-prone areas. Battery backup systems paired with solar may qualify for the 30% federal solar tax credit. Check with your tax advisor and your state’s energy office for current incentives.
Get at least 3 quotes from licensed installers. Prices for the same unit and installation can vary by $2,000–$4,000 between contractors. Shop in the off-season (spring and fall) when demand is lower. Ask each installer if they have any current promotions — manufacturers like Generac run installer incentives periodically.
Yes, particularly in outage-prone markets. Studies suggest standby generators add $500–$1,500 in home value per $1,000 invested in hurricane and storm-prone regions. In low-outage areas the return is smaller. It also helps sell a home faster — buyers in Florida or the Northeast see a generator as a major plus.
Know Your Size.
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from Local Installers.
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