Compare calculators

Both calculators run independently — change the inputs on either side to compare results.

Solar Panel System Sizing Calculator

Find out exactly how many solar panels your home needs to cover its electricity usage. Enter your monthly consumption, local sun hours, panel wattage, and system efficiency to get a panel count.

Monthly Electricity Usage (kWh)

Peak Sun Hours per Day (hours)

System Efficiency

Panel Wattage

Fill in the required fields to see your result.

Solar Energy

Solar Panel System Sizing Calculator

Calculate exactly how many solar panels your home needs based on your electricity bill, local sun exposure, panel wattage, and desired offset. Ideal for homeowners planning a rooftop PV installation.

Average monthly electricity use (kWh)

Peak sun hours (daily average) (h/day)

Share of usage to offset (%)

System losses (inverter, wiring, soiling, heat) (%)

Panel power rating (W)

Solar panels needed

21 panels

9.33

Lean sizingStandard full offsetLow-sun sizingOversized or low-sun

9.33: 7-10 W per monthly kWh is the normal range for a 100% offset at 4.5-5.5 sun hours. The example (9.3 W/kWh: 21x400W panels for 900 kWh) sits here.

This is installed watts per kWh of monthly usage; the formula's own math ties panel count to your offset target, sun hours, and losses, with ~7-13 W per monthly kWh being typical.

Key differences

	Solar Panel System Sizing Calculator	Solar Panel System Sizing Calculator
Category	Solar Energy	Solar Energy
Inputs required	4	5
Result	Number of Panels Needed (panels)	Solar panels needed (panels)
What it does	Find out exactly how many solar panels your home needs to cover its electricity usage. Enter your monthly consumption, local sun hours, panel wattage, and system efficiency to get a panel count.	Calculate exactly how many solar panels your home needs based on your electricity bill, local sun exposure, panel wattage, and desired offset. Ideal for homeowners planning a rooftop PV installation.