Ohm's Law Calculator (V, I, R, P) | Precision AGL Academy

Ohm's Law Calculator

Enter any two of voltage, current, resistance and power. Get the other two.

About this calculator

Everything on an airfield series circuit starts here. Pick the two values you know, choose your units, and the tool solves the rest with the formulas shown. It then runs the same resistance across each CCR brightness step, so you can see how voltage and power change from B1 to full brightness.

AGL examples

One tap fills in a typical airfield case. The two CCR examples treat kVA as an equivalent resistive load.

Known Values

I know

Current

Resistance

Values must be greater than 0. The CCR step table for the same resistance is on the next tab.

Report details

Label / Reference (for report)

Item (for report)

Same Resistance at Each CCR Step

Circuit class and steps

Resistance is held at the value solved on the Calculate tab. That is right for cable. Lamp filaments and LED loads change resistance with current, so treat them as a guide only. The 20 A steps are scaled in proportion to the 6.6 A steps. IEC 61822 covers 6.6 A CCRs only, so confirm 20 A steps against the CCR data sheet.

Step	Current	Voltage	Power	Power bar	% of full power

Calculator #52 | Rev. 1.3 | 25 Oct 2026

Engineering reference tool for planning and training. Applies to resistive circuits. For reactive loads use impedance and power factor. Results do not replace the project design or the applicable standards. See the Legal Notice.

Method & Reference

The twelve Ohm's law formulas

Two of the four quantities fix the other two. Each row below shows the three ways to find one quantity, depending on what you already know.

Formula table

To find	From V and I	From V and R	From I and R
Voltage V	—	—	I × R
Current I	—	V ÷ R	—
Resistance R	V ÷ I	—	—
Power P	V × I	V² ÷ R	I² × R

To find	From P and V	From P and I	From P and R
Voltage V	—	P ÷ I	√(P × R)
Current I	P ÷ V	—	√(P ÷ R)
Resistance R	V² ÷ P	P ÷ I²	—

Why it matters on an airfield

A series circuit carries the same current through every fixture, set by the CCR step. The voltage the CCR must supply is that current times the total resistance, and the heat lost in the cable is I² × R. Because loss follows the square of current, it falls to about 18 % of the full-brightness value at 2.8 A on a 6.6 A circuit.

V = I × R P_loss = I² × R

Worked example

A 4 km primary loop of #8 AWG has about 8.24 Ω of resistance at 20 °C. It carries 6.6 A at full brightness.

Item	Value
Known	I = 6.6 A, R = 8.24 Ω
Voltage drop, V = I × R	54.38 V
Cable loss, P = I² × R	358.9 W
Same cable at 2.8 A (B1)	23.07 V, 64.6 W
Loss at B1 vs full brightness	18.0 %

What this tool does not do

It treats the circuit as purely resistive. It does not handle reactive loads, power factor or temperature change of resistance. For those, use the Series Circuit Impedance and Circuit Power Factor calculators.

Ohm's Law for Airfield Circuits: Frequently Asked Questions

Quick answers on how the calculator solves V, I, R and P and applies them to CCR steps.

What does the Ohm's Law Calculator do?

You enter any two of voltage, current, resistance and power, choose your units, and it solves the other two with the formulas shown. It then holds the solved resistance constant and shows voltage and power at each CCR brightness step.

Which Ohm's law formulas does it use?

V = I × R, I = V ÷ R and R = V ÷ I, with power as P = V × I, P = I² × R or P = V² ÷ R. When power is one of the known values it uses forms such as I = P ÷ V, R = P ÷ I², I = √(P ÷ R) and V = √(P × R).

Why does Ohm's law matter on an airfield series circuit?

A series circuit carries the same current through every fixture, set by the CCR brightness step. The voltage the CCR must supply is that current times the total resistance, and the heat lost in the cable is I² × R. Because loss follows the square of current, it falls to about 18 % of the full-brightness value at 2.8 A on a 6.6 A circuit.

What CCR brightness steps does the step table use?

For the 6.6 A class, 5-step: 2.8, 3.4, 4.1, 5.2 and 6.6 A; 3-step: 4.8, 5.5 and 6.6 A. For the 20 A class, 5-step: 8.5, 10.3, 12.4, 15.8 and 20 A; 3-step: 14.5, 16.7 and 20 A. The table shows current, voltage, power and the percentage of full-brightness power for each step. The 6.6 A steps are the standard CCR presets. The 20 A steps are scaled from them in proportion, so confirm them against the CCR data sheet.

Can you show a worked example for cable loss?

A 4 km primary loop of #8 AWG has about 8.24 ohm of resistance at 20 °C. At 6.6 A the voltage drop is 54.38 V and the cable loss is 358.9 W. At 2.8 A (B1) the same cable drops 23.07 V and loses 64.6 W, which is 18.0 % of the full-brightness loss.

Can I use it for lamps, LED fixtures or reactive loads?

The calculator treats the circuit as purely resistive. The step table holds resistance constant, which suits cable but not lamp filaments or LED loads, whose resistance changes with current, so treat those results as a guide only. For reactive loads use impedance and power factor, for example the Series Circuit Impedance and Circuit Power Factor calculators.

How do the CCR kVA examples work?

The two CCR examples, 10 kVA at 6.6 A and 15 kVA at 20 A, treat the kVA rating as an equivalent resistive load, so the kVA value is entered as power in kW. This gives an equivalent voltage and resistance as a planning guide, not a circuit design.

Important Notice, Disclaimer & Limitation of Liability

Please read before relying on any content on this page or on any result or record produced by it.

Specific to this page: Applies to the Ohm's Law Calculator (calculator), including its PDF reports.

Calculated results. Results, tables, charts, status indicators (such as “OK”, “within limit” or “pass”/“fail”), recommended or selected values and the example presets on this page are first-pass planning and training estimates calculated in your browser from the values you enter, using simplified formulas, generic tables and typical values. They do not take account of every factor of a real installation, may contain errors or rounding differences, and are not a design, specification, selection, sizing, procurement or acceptance decision. A competent person must check them against the approved design, the manufacturer’s data and the applicable standard before any use. “Recommended” means an indicative estimate, not an endorsement of any rating, product or supplier.

Electrical values. Voltage, current, resistance, impedance, power, power factor, voltage drop, loss, load, capacity and efficiency figures depend on cable data, temperature, connector and transformer losses, CCR type, tolerances and other site conditions that a simplified calculation cannot fully capture. Default and example values are typical only. Do not rely on a result to load, energise, re-rate, tap or modify any circuit, CCR, cable or transformer.

Reports, downloads and printouts. PDF reports, CSV files and printed pages produced by this tool are uncontrolled working records generated in your browser. They are not approved designs, drawings, controlled documents, certificates, permits or regulatory records. Calculator numbers, revision labels, dates, project names, signature or approval fields on them are layout only and carry no authority unless made under your own approved document-control system. You must not present an output as an approved, verified or certified document. If you enter personal or confidential information, you are responsible for handling any exported file lawfully, including under the Digital Personal Data Protection Act, 2023.

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Standards and regulations. References to ICAO, FAA, IEC, IEEE, ISO, BIS (IS), DGCA, AAI and other documents are paraphrased summaries for orientation. They are not official text, may be incomplete or superseded, and do not state what any airport, project or regulator requires. Always consult the current official editions and the controlling project specification. Using this tool, or following its output, does not guarantee compliance with any law, standard or approval, and nothing on this page states that any airport, product or project complies or does not comply.

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Notice v2.9 · 27 October 2026 · Full terms: Legal & Disclaimer

Ohm's Law Calculator

Known Values

Report details

Same Resistance at Each CCR Step

The twelve Ohm's law formulas

Formula table

Why it matters on an airfield

Worked example

What this tool does not do

Ohm's Law for Airfield Circuits: Frequently Asked Questions

Related Knowledge Hub Resources

Primary Cable Resistance

Cable Voltage Drop

Circuit Voltage

AGL Toolkit

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Important Notice, Disclaimer & Limitation of Liability