Calculate cost per watt, solar price per watt after incentives, or electricity running cost from power, hours, rate, and size for quick comparisons.
Related Calculators
Cost Per Watt Formula
The calculator uses three formulas, one for each mode.
Price per watt:
PPW = Total Cost / Watts
Solar quote with incentives:
Net PPW = (Gross Cost * (1 - Tax Credit %) - Rebate) / System Watts
Running electricity cost:
Daily Cost = Watts * Hours per Day / 1000 * Rate
- Total Cost: purchase price in dollars.
- Watts: rated power, converted from W, kW, or MW.
- Gross Cost: solar quote before incentives.
- Tax Credit %: percentage incentive such as the 30% federal credit.
- Rebate: fixed dollar incentive applied after the percentage credit.
- System Watts: either the entered system size or panels times watts per panel.
- Hours per Day: average daily run time, capped at 24.
- Rate: electricity price in dollars per kilowatt-hour.
The Price per watt tab divides any cost by any wattage to give dollars per watt and dollars per kilowatt. The Solar quote tab does the same but adds a percentage credit and fixed rebate, then flags whether the gross figure is low, typical, or high. The Running cost tab converts watts and hours into kWh, then multiplies by your electricity rate to project daily, monthly, and yearly cost.
Reference Tables
Use these as sanity checks against your own inputs.
| Residential Solar PPW (gross) | Interpretation |
|---|---|
| Under $3.00/W | Low, verify equipment and warranty. |
| $3.00 to $4.50/W | Typical US residential range. |
| $4.50 to $5.50/W | High, ask for an itemized quote. |
| Over $5.50/W | Very high, get competing bids. |
| Appliance | Watts | Cost at 4 hrs/day, $0.17/kWh |
|---|---|---|
| LED bulb | 9 | $0.19/month |
| Incandescent bulb | 75 | $1.55/month |
| Laptop | 150 | $3.10/month |
| Microwave | 1,000 | $20.69/month |
| Space heater | 1,500 | $31.04/month |
| Central AC | 3,500 | $72.42/month |
| EV charger | 7,200 | $148.97/month |
Worked Examples
Example 1: Solar quote. A 6 kW system is quoted at $19,800 gross. The federal tax credit is 30% and the utility offers a $500 rebate.
- Gross PPW = 19,800 / 6,000 = $3.30/W
- Net cost = 19,800 × 0.70 − 500 = $13,360
- Net PPW = 13,360 / 6,000 = $2.23/W
Example 2: Running cost. A 1,500 W space heater runs 5 hours per day at $0.17/kWh.
- Energy = 1,500 × 5 / 1,000 = 7.5 kWh/day
- Daily cost = 7.5 × 0.17 = $1.28
- Monthly cost ≈ $38.80
FAQ
Should I compare quotes using gross or net price per watt?
Use gross PPW to compare installers on equal footing. Incentives vary by location and tax situation, so net PPW reflects your wallet but not the installer's pricing.
Does price per watt include the inverter and installation?
For solar, gross system cost should be the full turnkey price: panels, inverter, racking, wiring, permits, and labor. If a quote excludes any of these, the PPW will look artificially low.
Why is monthly cost calculated with 30.4375 days?
That is the average days per month over a year (365 / 12). It avoids the swing between 28 and 31 day months.
What electricity rate should I use?
Check the supply and delivery charges on your utility bill and add them. The default of $0.17/kWh is near the US residential average but varies widely by state.
Cost Per Watt Formula
The basic cost per watt formula divides the total cost by the total watts of power or system capacity.
Cost\ Per\ Watt = Total\ Cost / Watts
- Cost Per Watt is the price for each watt of capacity, usually shown as dollars per watt.
- Total Cost is the full purchase price or system price.
- Watts is the total power or system size in watts.
For solar quotes, the calculator can compare gross price per watt and net price per watt after a percentage incentive and any fixed rebate.
Gross\ Price\ Per\ Watt = Gross\ System\ Cost / System\ Watts
Net\ Cost = Gross\ System\ Cost * (1 - Incentive\ Percent / 100) - Fixed\ Rebate
Net\ Price\ Per\ Watt = Net\ Cost / System\ Watts
- Gross System Cost is the quoted price before incentives or rebates.
- System Watts is the solar system size in watts.
- Incentive Percent is the tax credit or percentage discount.
- Fixed Rebate is a dollar amount subtracted after the percentage incentive.
- Net Cost is the remaining cost after incentives are applied.
If you enter solar panels instead of a known system size, the calculator first finds total system watts.
System\ Watts = Number\ Of\ Panels * Watts\ Per\ Panel
- Number Of Panels is the count of solar panels in the system.
- Watts Per Panel is the rated wattage of one panel.
For running electricity cost, the calculator converts watts to kilowatt-hours and multiplies by your electricity rate.
Daily\ kWh = Watts * Hours\ Per\ Day / 1000
Daily\ Cost = Daily\ kWh * Electricity\ Price
Monthly\ Cost = Daily\ Cost * 30.4375
Yearly\ Cost = Daily\ Cost * 365
- Watts is the appliance power draw.
- Hours Per Day is daily use time.
- Daily kWh is daily energy use in kilowatt-hours.
- Electricity Price is your utility rate in dollars per kWh.
The price per watt tab is best for a direct equipment or system price. The solar quote tab is best when incentives or panel counts matter. The running cost tab is for estimating electricity use over time, not purchase price per watt.
Typical Cost Per Watt Ranges
Cost per watt depends on what you are measuring. A finished installed system usually costs more per watt than the panels alone.
| Item or system | Common result | What it usually means |
|---|---|---|
| Solar panel only | Often under installed system pricing | Does not include inverter, mounting, labor, design, permitting, or markup. |
| Residential solar quote | About $3.00 to $4.50 per watt is a common quote range | Compare equipment, roof work, batteries, financing, and warranty terms before judging the quote. |
| Low solar quote | Below about $3.00 per watt | May be competitive, but check what is included and whether the price is before or after incentives. |
| High solar quote | Above about $4.50 per watt | May include adders such as batteries, complex roof work, electrical upgrades, or higher financing costs. |
Common Appliance Running Cost Inputs
Use the running cost mode when you want to estimate the electricity cost of using an appliance.
| Appliance | Typical wattage | Notes |
|---|---|---|
| LED bulb | 9 W | Low power use, but total cost depends on hours used. |
| Laptop | 150 W | Actual draw may be lower during light use. |
| Microwave | 1000 W | High wattage, but usually used for short periods. |
| Space heater | 1500 W | Can add noticeable cost if used for many hours per day. |
| EV charger | 7200 W | Cost depends heavily on charge time and electricity rate. |
Example Calculations
Example 1: Solar price per watt
You have a solar quote for $19,250 and the system size is 5.5 kW.
First convert kilowatts to watts:
5.5\ kW * 1000 = 5500\ W
Then divide the total cost by watts:
19250 / 5500 = 3.50
The result is $3.50 per watt.
Example 2: Running cost
You use a 1500 W space heater for 4 hours per day, and electricity costs $0.17 per kWh.
Daily\ kWh = 1500 * 4 / 1000 = 6
Daily\ Cost = 6 * 0.17 = 1.02
Monthly\ Cost = 1.02 * 30.4375 = 31.05
The estimated cost is $1.02 per day, or about $31.05 per month.
FAQ
Is cost per watt the same as cost per kilowatt-hour?
No. Cost per watt measures purchase price or installed capacity. For example, a solar system quote can be compared in dollars per watt. Cost per kilowatt-hour measures electricity usage or energy cost over time. Utility bills usually charge by kilowatt-hour, not by watt.
Should solar price per watt be calculated before or after incentives?
Both numbers can be useful. Gross price per watt shows the quote before incentives and is often better for comparing installer pricing. Net price per watt shows your estimated cost after tax credits or rebates. If you compare quotes, make sure every quote is being compared on the same basis.
Why does the calculator convert kW to watts?
Cost per watt uses watts in the denominator. Since many solar systems are listed in kilowatts, the calculator converts kW to W by multiplying by 1000. For example, 6.2 kW is 6200 W.
