Solar Panel Calculator Online — Free Solar Panel Calculator Tool
CodexFuse Team · 2026-11-05T23:46:50.232Z · 8 min read min read
How many solar panels does your home need? Enter daily kWh, peak sun hours and panel watts into the free solar panel calculator and get your exact count.
A solar panel calculator answers one question before you spend a rupee on panels: how many do you actually need? Feed it your daily electricity use, your area's peak sun hours and the wattage of the panels you plan to buy, and it returns a panel count, a system size and the daily output you can expect. CodexFuse's free solar panel calculator does exactly that in your browser, with no install.
Most people size a solar system by guessing — a neighbour installed 12 panels, so 12 must be right. Too few panels and you keep paying the grid; too many and you paid for capacity your roof never uses.
How many solar panels do I need?
Divide your daily use by what one panel produces in a day: panels equals daily kWh times 1,000, divided by peak sun hours times panel watts, rounded up. A home using 30 kWh a day, with 5 peak sun hours and 400W panels, needs 30,000 divided by (5 times 400) — 15 panels, a 6,000W system.
The formula has three inputs, and each one is easy to get wrong.
Daily electricity use in kWh
Take the kWh figure from your electricity bill and divide by 30. A 900 kWh monthly bill is 30 kWh a day; a 1,500 kWh bill is 50 kWh a day. Use a yearly average if your bill swings with the seasons.
Peak sun hours
A peak sun hour is one hour of full-intensity sunlight (1,000W per square metre), not one hour of daylight. Typical values run 3–4 hours in cloudier regions, 4–5 in mid-latitudes, 5–6 across the Sun Belt and 6–7 in the sunny Southwest. Your installer or a solar map can give you the local figure; guessing it high is the most common way to undersize a system.
Panel wattage
400W is the common modern size, and the calculator accepts anything up to 1,000W. Higher-wattage panels mean fewer panels for the same system size, which matters when roof space is the constraint.
How the solar panel calculator works
The solar panel calculator runs three steps and shows every one of them. System size: daily kWh times 1,000 divided by peak sun hours. Panel count: system watts divided by panel watts, rounded up. Daily output: panels times panel watts times sun hours divided by 1,000.
Three details from the live tool are worth knowing:
- One-tap presets: presets for common homes — 10 kWh a day, 30 kWh a day at 4 sun hours, and 5 kWh a day at 6 sun hours with 300W panels — so you can sanity-check a result before typing your own numbers.
- Generous input limits: daily use up to 10,000 kWh, sun hours up to 12 and panel watts up to 1,000. Commas are ignored, so 1,000 works the same as 1000.
- Copy in one click: the result copies to your clipboard, handy when you are pasting the numbers into a quote request or a spreadsheet.
Size on your highest-use month, not your annual average. A system sized for a mild spring month leaves you buying grid power all summer.
A worked example: the Ahmed family's 900 kWh home
Meet the Ahmeds — a fictional family of four. Their bill averages 900 kWh a month, their area gets 5 peak sun hours, and their installer quoted 400W panels.
Step 1 — daily use: 900 kWh divided by 30 days is 30 kWh a day. Step 2 — system size: 30 times 1,000 divided by 5 sun hours is 6,000W. Step 3 — panel count: 6,000 divided by 400 is exactly 15 panels. Step 4 — daily output: 15 panels times 400W times 5 sun hours divided by 1,000 is 30 kWh a day — a perfect match on paper.
Here is where the honest arithmetic starts. The calculator sizes on nameplate ratings with no efficiency factor, so 15 panels is the minimum for perfect conditions. Real systems lose roughly 20% to inverter conversion, wiring, panel heat, soiling and shading — so the Ahmeds need about 18 or 19 panels to actually cover 30 kWh a day, not 15.
| Monthly bill | Daily use | Panels (calculator) | System size | Panels with 20% losses |
|---|---|---|---|---|
| 500 kWh | 16.67 kWh | 9 | 3,333W | 11 |
| 900 kWh | 30 kWh | 15 | 6,000W | 18 |
| 1,500 kWh | 50 kWh | 25 | 10,000W | 30 |
| 2,000 kWh | 66.67 kWh | 34 | 13,333W | 41 |
All figures above assume 5 peak sun hours and 400W panels. Change either number in the solar panel calculator and the count moves with it.
While solar cuts what you pay the grid, most small businesses still bleed money on IT — separate hosting, email, security and backup subscriptions, each with its own surprise renewal. CodexFuse replaces them with one fully managed platform on pay-as-you-go credits.
Get Started with CodexFuseWhat the calculator does not tell you
A panel-count tool is a starting point, not a quote.
- No system losses: the tool sizes on perfect-condition ratings, so treat its panel count as a floor, not a final number.
- No roof or shading analysis: it does not know your roof's angle, orientation, usable area or whether a tree shades it at 4 p.m.
- No costs or payback: it answers "how many panels", not "how much will it cost" or "when does it pay for itself". Panel prices, installation, inverters, batteries and local incentives all sit outside the tool.
- Login may be required: the tool page asks you to log in to use it, so keep a free CodexFuse account handy.
Never sign a solar contract based on a single online calculator. Use the panel count to check an installer's quote — if their number is far from yours, ask them to show their working.
Cutting the other bill: your home office IT costs
The Ahmeds' story has a second half: one of them runs a small online business from the spare room, and while solar attacks the power bill, the business still pays separately for hosting, business email, security and backups — four subscriptions, four renewal dates, four surprise price rises a year.
On CodexFuse the workflow is concrete. First, list every IT subscription the business pays for. Second, move the website, email and backups onto the platform as managed services, where setup and maintenance are handled for you. Third, pay with credits — topped up as you go, spent only on what you use.
The decision rule is simple: if your IT stack is four or more separate subscriptions and nobody enjoys maintaining servers, the managed route costs less in money and far less in time. If you genuinely enjoy server administration, stay where you are.
Running the numbers on other decisions? Try the rent vs buy calculator before your next move, the ad budget calculator if your business spends on ads, and the bandwidth calculator and date calculator for quick conversions.
Frequently Asked Questions
How many solar panels do I need for my home?
Divide your daily use by what one panel makes: panels equals daily kWh times 1,000 divided by (peak sun hours times panel watts), rounded up. A 900 kWh monthly bill at 5 sun hours with 400W panels needs 15 panels on paper, or around 18 once real-world losses are counted.
What is a peak sun hour?
One hour of full-intensity sunlight at 1,000W per square metre — not one hour of daylight. Five peak sun hours means the same energy as five hours at full noon sun, spread across the day.
Does the solar panel calculator account for system losses?
No. It sizes on nameplate ratings with no efficiency factor, so its panel count is the minimum for perfect conditions. Real systems lose roughly 20% to inverter conversion, wiring, heat, soiling and shading — add about 20% more panels, or enter fewer sun hours, for a realistic figure.
How do I find my daily kWh?
Take the kWh figure from your electricity bill and divide by 30 — a 900 kWh monthly bill is 30 kWh a day. Use a yearly average if your bill varies by season.
What panel wattage should I enter?
400W is the common modern residential size and a safe default. If your installer quoted a different wattage, enter that instead.
Is the solar panel calculator really free?
Yes — it runs in your browser with no install and no payment. The tool page asks you to log in to use it, so create a free CodexFuse account first.
Run your numbers, then fix the bill you can control today
Open the free solar panel calculator, enter your daily kWh from your last bill, your local peak sun hours and 400W panels, and write down the panel count — then add 20% for real-world losses before you talk to any installer.
And while you are cutting the power bill, cut the IT bill the same way. Move your hosting, business email, security and backups to CodexFuse today: one fully managed platform, paid on credits only for what you use. Get started with CodexFuse and stop paying four different companies to run one small business.
