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DC Voltage Drop Calculator
Works out the cable size a low-voltage DC run needs to stay within a voltage drop limit, and the power lost as heat.
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Enter your figures and press Calculate.
In short
DC Voltage Drop Calculator is a free online tool on inputtesthub.com that works out the cable size a low-voltage DC run needs to stay within a voltage drop limit, and the power lost as heat. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.
How to use the DC Voltage Drop Calculator
- Enter your figures in the input fields.
- The result updates as you type, together with the full working.
- Check the breakdown table to see exactly how the number was reached.
About the DC Voltage Drop Calculator
The DC Voltage Drop Calculator works out the cable size a low-voltage DC run needs to stay within a voltage drop limit, and the power lost as heat. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Sizing cable between solar panels and a charge controller.
- Wiring a 12 V system in a van or boat.
- Checking why an inverter cuts out under load.
Details
| 3% of 12 V | Only 0.36 V |
|---|---|
| Same power at 48 V | A quarter of the current |
| Drop scales with | Current and length |
| Loss becomes | Heat in the cable |
The maths behind it
This tool uses Drop = current × resistance per metre × length × 2, because the current travels out and back. The cable is sized so that drop stays within the chosen percentage of system voltage. Every intermediate value is shown on screen, so the result can be checked by hand.
Low-voltage DC is where cable size stops being a formality. The same 300 W needs 25 A at 12 V but 1.3 A at 230 V. If the cable comes out impractically large, raising the system to 24 or 48 V is usually the cheaper fix.
Frequently asked questions
Is the DC Voltage Drop Calculator free, or is there a paid tier?
Free, unlimited, and no email address required. You can use it a hundred times a day and nothing changes.
Is what I paste into the DC Voltage Drop Calculator stored?
No. The DC Voltage Drop Calculator runs entirely in your browser using JavaScript. Your input never reaches inputtesthub.com or any third party — open your browser's Network tab while you use it and you will see no request go out.
How is the result calculated?
It uses Drop = current × resistance per metre × length × 2, because the current travels out and back. The cable is sized so that drop stays within the chosen percentage of system voltage. The full working is printed under the result, so you can follow every step rather than trusting a black box.
Who is the DC Voltage Drop Calculator for?
The jobs it is built for: sizing cable between solar panels and a charge controller. Wiring a 12 V system in a van or boat. Checking why an inverter cuts out under load. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
What do people usually get wrong here?
Low-voltage DC is where cable size stops being a formality. The same 300 W needs 25 A at 12 V but 1.3 A at 230 V. If the cable comes out impractically large, raising the system to 24 or 48 V is usually the cheaper fix.
What are the key numbers for the DC Voltage Drop Calculator?
3% of 12 V is Only 0.36 V. Same power at 48 V is A quarter of the current. Drop scales with is Current and length. These are printed on the page itself, so you do not have to take them on trust.
How precise is the result?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.
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