---
title: Off-Grid Solar Battery Bank Sizing Guide + Free Calculator
siteUrl: https://logzly.com/offgridgreen
author: offgridgreen (Off-Grid Green Living)
date: 2026-07-25T20:51:35.686741
tags: [offgrid, solarbattery, diy]
url: https://logzly.com/offgridgreen/off-grid-solar-battery-bank-sizing-guide-free-calculator
---


Struggling to size your off‑grid solar battery bank? Follow this exact formula and download the free calculator to get the right amp‑hour count instantly—no guesswork, no wasted money.  
Below you’ll find the exact steps I used to stop guessing and start calculating, plus a link to the ready‑to‑use spreadsheet that saved me thousands.

## Off‑Grid Solar Battery Bank Sizing: Step‑by‑Step Formula

**Figure out your daily load** – List every device you plan to run, note its wattage, and estimate how many hours you’ll use it each day. Add them up and you get total watt‑hours per day. For my cabin it was about 1,200 Wh.  

**Convert to amp‑hours** – Divide the daily watt‑hours by your system voltage (most off‑grid setups use 12 V, 24 V, or 48 V). I used 24 V, so 1,200 Wh ÷ 24 V = 50 Ah per day.  

**Decide on days of autonomy** – Think about the longest stretch of cloudy days you can tolerate. I chose 3 days, so 50 Ah × 3 = 150 Ah.  

**Apply depth‑of‑discharge** – Choose a safe DoD for your battery type. Lead‑acid should stay around 50 %, lithium can go to 80 % or more. Using lead‑acid, 150 Ah ÷ 0.5 = 300 Ah total capacity needed.  

**Select battery size and count** – Look at the amp‑hour rating of the batteries you like. If you pick 100 Ah units, you’ll need three of them in parallel (100 Ah × 3 = 300 Ah). The spreadsheet on Off‑Grid Hacks lets you plug in different numbers to see how many you’ll need.  

While you’re at it, consider the **best battery type for off‑grid solar storage**. Lead‑acid is cheap but heavy and loses capacity over time. Lithium‑ion costs more upfront but gives you more usable capacity and lasts longer. For a tiny cabin, I went with lithium after doing the math, because the extra upfront cost paid off in fewer batteries and less weight.  

If you’re still unsure, the **solar battery bank size calculator for tiny cabin** I posted does all the steps automatically. Just enter your daily watt‑hours, voltage, desired days of autonomy, and battery type, and it spits out the amp‑hour total and how many batteries you need. It’s been a lifesaver for friends who are just getting started.  

Getting a solid number for your battery bank feels like finally turning the lights on after a long night of stumbling in the dark. No more guessing, no more wasted cash, just a clear plan that lets you enjoy your off‑grid life without fear of a sudden blackout. If this guide helped you, feel free to share it with anyone you know who’s planning a cabin, a tiny house, or any off‑grid adventure.  

If you want more quick, hands‑on guides like this, subscribe to the Off‑Grid Hacks newsletter. I’ll drop new tips, spreadsheets, and real‑world stories straight into your inbox. And hey, if you think a buddy could use a better battery‑sizing plan, pass this post along. Happy building!