kW to Solar Panels Calculator

How many panels for 5 kW? 8 kW? 10 kW? Enter any system size — get your panel count instantly.

Convert kW to panels

Desired system size?

Panel wattage?

Number of panels

20 panels

Actual system size8.00 kW

Total roof area388 sq ft (36.0 m²)

Cost range (before ITC)$20,000 – $25,600

After 30% tax credit$14,000 – $17,920

Link copied to clipboard

How to Use This Calculator

Enter your desired system size in kW

Type the total system capacity in kW that you want to install. If you already have a quote from an installer that says "8 kW system" — enter 8. If you don't know your system size yet, use the Solar Panel Calculator to calculate it from your electricity bill, then come back here.

Select panel wattage

Choose the rated wattage of each panel. Modern residential panels range from 350W to 450W. If your installer has specified a panel model, look up its rated power on the spec sheet. The calculator rounds up to whole panels — you can't install 0.7 of a panel, so the actual system size is always slightly higher than your target.

Read the results

The calculator shows panel count, actual system size (always equal to or slightly above your target), total roof area, and an estimated installed cost range with and without the 30% federal tax credit. The cost range reflects typical US installer pricing in 2026 — actual quotes vary by region, equipment, and installer.

The Formula

Panels needed = CEILING(System kW × 1,000 ÷ Panel wattage) Actual kW = Panels × Panel wattage ÷ 1,000 Roof area (sq ft) = Panels × Panel area per panel Cost range = Actual kW × 1,000 × ($2.50 to $3.20 per watt) After 30% ITC = Cost × 0.70

The CEILING function rounds up to the nearest whole panel. For an 8 kW system with 400W panels: 8,000 ÷ 400 = exactly 20 panels. For a 10 kW system with 400W panels: 10,000 ÷ 400 = exactly 25 panels. For a 7 kW system with 400W panels: 7,000 ÷ 400 = 17.5, rounded up to 18 panels = 7.2 kW actual.

Quick Reference Table

System size to panel count (400W panels)

3 kW8 panels — 155 sq ft

4 kW10 panels — 194 sq ft

5 kW13 panels — 252 sq ft

6 kW15 panels — 291 sq ft

8 kW20 panels — 388 sq ft

10 kW25 panels — 485 sq ft

12 kW30 panels — 582 sq ft

15 kW38 panels — 737 sq ft

FAQ

How many solar panels do I need for a 5 kW system? ▼

With 400W panels: 5,000 ÷ 400 = 12.5, rounded up to 13 panels (5.2 kW actual). With 350W panels: 5,000 ÷ 350 = 14.3, rounded up to 15 panels (5.25 kW actual). With 450W panels: 5,000 ÷ 450 = 11.1, rounded up to 12 panels (5.4 kW actual). The actual installed size is always slightly above the target due to rounding up to whole panels.

How many solar panels do I need for a 10 kW system? ▼

With 400W panels: exactly 25 panels. With 350W panels: 29 panels (10.15 kW). With 450W panels: 23 panels (10.35 kW). A 10 kW system typically covers a home using 1,200-1,500 kWh/month in an average US location. It requires about 450-550 sq ft of south-facing roof space.

Why is the actual system size slightly different from what I entered? ▼

Solar panels come in fixed wattages — you can't cut one in half. So the calculator always rounds up to the next whole panel. This means the actual installed capacity is equal to or slightly above your target. An 8 kW target with 350W panels requires 23 panels × 350W = 8.05 kW. The small overage is normal and beneficial — you never want to undersize.

Are the cost estimates accurate? ▼

The $2.50-$3.20/W range represents typical US residential solar installation costs in 2026, including panels, inverter, mounting hardware, wiring, labor, permits, and inspection. Regional variation is significant — California, Massachusetts, and New York tend to be 15-25% above average; Texas, Florida, and Arizona tend to be at or below average. Get 3+ quotes from local installers for accurate pricing.

What kW system size is right for an average American home? ▼

The average US home uses about 900 kWh/month. In a location with 4.5 peak sun hours and 86% system efficiency, a 7-8 kW system offsets 100% of that usage. With an EV charger, expect to need 10-12 kW. All-electric homes with heat pumps often need 12-15 kW. The most accurate sizing comes from your actual electricity bill — use the Solar Panel Calculator to enter your bill directly.