The Voltage Drop Calculator is a free tool that helps you calculate voltage drop using the formula Vdrop = 2 x I x (resistivity x length / area). Enter your values above and press Calculate to get voltage drop, drop instantly, with a full step-by-step breakdown.
What is the Voltage Drop Calculator?
The voltage drop calculator is a free online tool that helps you calculate voltage drop quickly and accurately. It applies the standard formula Vdrop = 2 x I x (resistivity x length / area) to the values you enter and, when you press Calculate, displays the result together with a clear, step-by-step explanation of how the answer was reached.
Also known as: voltage drop formula.
How to use the Voltage Drop Calculator
- Enter current and cable length.
- Enter conductor resistivity and area.
- See the voltage drop.
Formula used
The voltage drop calculator is based on this formula:
Vdrop = 2 x I x (resistivity x length / area)Each term in the formula corresponds to one of the inputs explained below. The calculator performs the arithmetic for you and shows every step so you can check the working by hand if you wish.
Worked example
Suppose you enter 10A, 30m, 2.5mm2 Cu. The calculator works as follows:
| Inputs | 10A, 30m, 2.5mm2 Cu |
|---|---|
| Working | 2x10x(0.0175x30/2.5) |
| Result | about 4.2 V |
Step-by-step calculation
- Apply the formula:
Vdrop = 2 x I x (resistivity x length / area) - Substitute your values: 2x10x(0.0175x30/2.5)
- Read the result: about 4.2 V
Inputs explained
- Current (A) — the current used in the calculation.
- Cable length (one way) (m) — the cable length (one way) used in the calculation.
- Resistivity (ohm mm2/m) — the resistivity (ohm mm2/m) used in the calculation.
- Conductor area (mm2) — the conductor area used in the calculation.
- Supply voltage (V) — the supply voltage used in the calculation.
Understanding your result
- Voltage drop — the calculated voltage drop in V.
- Drop — the calculated drop in %.
Benefits and practical uses
The voltage drop calculator saves time and removes the risk of manual errors when you need to calculate voltage drop. It is useful for students, professionals and anyone who wants a fast, dependable answer. Results update the moment you press Calculate, work on any device, and can be copied or shared in a single click — and because the maths runs in your browser, your figures stay completely private.
Tips for an accurate result
- Keep all related inputs in the same units.
- Use the worked example above to confirm you are entering values in the right places.
- Review the assumptions below so the result fits your situation.
- Press Reset to clear everything and try a different scenario.
Common mistakes to avoid
- Entering values in the wrong unit (mismatched units give wrong answers).
- Leaving a required field empty — the calculator will ask you to fill it in.
- Rounding inputs too early, which can slightly change the result.
Assumptions and limitations
- Copper resistivity by default; single-phase two-wire.
Frequently asked questions
What voltage drop is acceptable?
Many codes recommend keeping total drop under 3-5% of supply voltage.
How do I use the Voltage Drop Calculator?
Enter your values in the fields, then press the Calculate button to see the result. Use Reset to clear the form and start again. Nothing is calculated until you click Calculate.
What formula does the Voltage Drop Calculator use?
It uses the standard formula: Vdrop = 2 x I x (resistivity x length / area). The full step-by-step working is shown with every result so you can verify it.
What information do I need to use the voltage drop calculator?
You need: current, cable length (one way), resistivity (ohm mm2/m), conductor area, supply voltage. Sensible example values are pre-filled so you can see how it works.
Is the Voltage Drop Calculator free to use?
Yes. Every DigiToolkit calculator is completely free, with no sign-up, no login and no usage limits.
Does the Voltage Drop Calculator work on mobile phones?
Yes. The calculator is mobile-first and works on phones, tablets and computers in any modern browser.
Do I need to install an app?
No. The voltage drop calculator runs directly in your web browser — there is nothing to download or install.
Is my data private when I use this calculator?
Yes. All calculations run inside your browser. The numbers you enter are never uploaded to a server or shared with anyone.
How accurate is the Voltage Drop Calculator?
It uses the generally accepted formula for voltage drop and computes to several decimal places. Results are accurate for the assumptions listed on this page.
Can I copy or share my result?
Yes. After calculating, use the Copy button to copy the result, or Share to copy the page link.
Why is nothing showing until I press Calculate?
By design, the calculator only computes when you press Calculate, so you can finish entering all your values first. Press Reset any time to clear everything.
What units does the Voltage Drop Calculator use?
It works with A, V, m, mm2. Keep your inputs in consistent units for an accurate result.