Ohm's Law Calculator

Live V = I R board that solves for voltage, current, or resistance, with a power twin and a decade load ladder so watts and load draw stay visible beside the triad.

Educational ideal ohmic literacy only. Not live-work advice, building-code design, or PCB layout. Mains and high-energy circuits need qualified people and proper ratings.

By Ahmet C. Toplutaş·Site owner & editor · Science tools

Last updated May 21, 2026 · Reviewed May 21, 2026 · Planning estimates only - not tax, medical, or investment advice

Close the V = I R triad

Ohm’s law links three circuit quantities for an ideal resistor: voltage V, current I, and resistance R. Know any two and the third is determined. That is the whole classroom triangle: V = I R, I = V / R, R = V / I.

This page’s framing is a solve-for triad, with a power twin (three P formulas) and a decade load ladder at fixed board voltage. It is not Newton’s F = m a weight/g board, not density’s material/SG ladder, and not the permutation identity peel.

Decision framing: “Which leg is missing, what power does that imply, and how would current change if the load were a decade higher or lower?”

Educational ideal ohmic literacy only. Not live electrical work advice, building-code design, or PCB layout. Mains and high-energy circuits need qualified people and proper ratings. See our disclaimers.

Power twin beside Ohm

Closing V, I, and R also closes electrical power. Homework often asks you to check P = V I, P = I² R, and P = V² / R. The twin shows all three so a transcription error on one formula stands out.

Load USB load, then Heater sketch. Watch power jump into the high-power narrative while the three P lines stay consistent.

Decade load ladder

Hold board voltage fixed and scan 1 Ω through 10 kΩ. Current and power fall as resistance rises. That ladder is the product beat: one supply, many possible loads, without retyping V each time.

Milli / base / kilo chips

Electronics homework mixes mA with kΩ constantly. Each field has milli / base / kilo chips so 20 mA and 10 kΩ enter as classroom numbers while the math stays in SI volts, amperes, and ohms.

What the panel actually computes

Ideal ohmic relations plus power identities.

V = I R I = V / R R = V / I P = V I = I² R = V² / R ladder: I(R) = V / R (fixed board V)

Where this hands off

After an ohmic sketch, hand off for other science literacy tools. Series/parallel networks and non-ohmic devices need more than a single V = I R line.

F = m a: Newton's law
Density ρ = m / V: density calculator
Pressure: pressure calculator
Speed: speed calculator

Worked scenarios

Scenario A: LED drop. 5 V and 20 mA solve R. Treat as a classroom series-resistor sketch; real LEDs are not ohmic.

Flip solve-for to voltage with the same I and R. The triad should reclose on ~5 V and the power twin should match.

Scenario B: USB load. 5 V at 2 A implies a low R and multi-watt P. Compare the ladder’s 1 Ω and 10 Ω rows at 5 V.

Scenario C: Heater sketch. 120 V across 10 Ω. High power narrative is intentional; mains work is not a DIY homework toy.

Scenario D: Sensor bias. 3.3 V and 10 kΩ with milli current display. Small-signal literacy without inventing a PCB.

Common mistakes

Mixing mA with A (or kΩ with Ω) without the prefix chips.
Treating LEDs, transistors, or motors as perfectly ohmic.
Using P = V I once and skipping the I² R / V² R cross-check.
Dividing by zero when R or I is blanked to nothing.
Confusing this board with Newton's law (mechanics) or a full circuit simulator.
Treating the sketch as permission to work on live mains.

How to use this panel

Load a preset or pick which of V, I, or R to solve.
Enter the two knowns and set milli / base / kilo chips.
Read the closed triad, power twin, and decade load ladder.
Share when you want URL state. Typing does not rewrite the address bar. Keep ideal ohmic assumptions in mind.

When not to stop at V = I R

Stop here for an ideal single-resistor homework close. Hand off for other science tools when the question is mechanics, density, or pressure. For multi-loop circuits, AC, or safety-critical design, use proper analysis tools and qualified review.

Newton's law: F = m a.
Density: density.
Pressure: pressure.

Frequently asked questions

How does this Ohm's law calculator work?

It solves V = I R for voltage, current, or resistance when you enter the other two (with optional milli/kilo prefixes). The board also shows electrical power P = V I and a decade load ladder of currents and watts at the same board voltage.

What is the power twin?

Once V, I, and R are closed, power can be written three ways: P = V I, P = I² R, and P = V² / R. The peel shows all three so homework cross-checks stay visible.

What is the decade load ladder?

It holds your solved (or known) voltage fixed and lists current and power for 1 Ω, 10 Ω, 100 Ω, 1 kΩ, and 10 kΩ loads. That shows how load resistance scales draw at one supply.

When is Ohm's law valid?

For ohmic resistors in the linear region, V and I stay proportional. Many real devices (LEDs, semiconductors, motors) are only approximately ohmic; treat this board as an ideal literacy sketch.

Why can I not divide by zero?

Solving I = V / R needs nonzero R, and R = V / I needs nonzero I. Those blocks prevent undefined homework results.

Is this safe for mains or PCB design?

No. It is educational circuit literacy only. Live electrical work, code compliance, and product design need qualified people, proper ratings, and safety practice. Do not use this as live-work advice.

How is this different from Newton's law or density?

Newton's law closes F = m a with a weight twin. Density solves ρ = m / V. This page is the V = I R triad with a power twin and a resistance decade ladder.

Sources

Loading…

Close the V = I R triad

Decision framing: “Which leg is missing, what power does that imply, and how would current change if the load were a decade higher or lower?”

Power twin beside Ohm

Load USB load, then Heater sketch. Watch power jump into the high-power narrative while the three P lines stay consistent.

Worked scenarios

Scenario A: LED drop. 5 V and 20 mA solve R. Treat as a classroom series-resistor sketch; real LEDs are not ohmic.

Flip solve-for to voltage with the same I and R. The triad should reclose on ~5 V and the power twin should match.

Scenario B: USB load. 5 V at 2 A implies a low R and multi-watt P. Compare the ladder’s 1 Ω and 10 Ω rows at 5 V.

Scenario C: Heater sketch. 120 V across 10 Ω. High power narrative is intentional; mains work is not a DIY homework toy.

Scenario D: Sensor bias. 3.3 V and 10 kΩ with milli current display. Small-signal literacy without inventing a PCB.

Common mistakes

Mixing mA with A (or kΩ with Ω) without the prefix chips.
Treating LEDs, transistors, or motors as perfectly ohmic.
Using P = V I once and skipping the I² R / V² R cross-check.
Dividing by zero when R or I is blanked to nothing.
Confusing this board with Newton's law (mechanics) or a full circuit simulator.
Treating the sketch as permission to work on live mains.

When not to stop at V = I R

Newton's law: F = m a.
Density: density.
Pressure: pressure.

Frequently asked questions

How does this Ohm's law calculator work?

What is the power twin?

Once V, I, and R are closed, power can be written three ways: P = V I, P = I² R, and P = V² / R. The peel shows all three so homework cross-checks stay visible.

What is the decade load ladder?

It holds your solved (or known) voltage fixed and lists current and power for 1 Ω, 10 Ω, 100 Ω, 1 kΩ, and 10 kΩ loads. That shows how load resistance scales draw at one supply.

When is Ohm's law valid?

For ohmic resistors in the linear region, V and I stay proportional. Many real devices (LEDs, semiconductors, motors) are only approximately ohmic; treat this board as an ideal literacy sketch.

Why can I not divide by zero?

Solving I = V / R needs nonzero R, and R = V / I needs nonzero I. Those blocks prevent undefined homework results.

Is this safe for mains or PCB design?

No. It is educational circuit literacy only. Live electrical work, code compliance, and product design need qualified people, proper ratings, and safety practice. Do not use this as live-work advice.

How is this different from Newton's law or density?

Newton's law closes F = m a with a weight twin. Density solves ρ = m / V. This page is the V = I R triad with a power twin and a resistance decade ladder.

Close the V = I R triad

Power twin beside Ohm

Decade load ladder

Milli / base / kilo chips

What the panel actually computes

Where this hands off

Worked scenarios

Common mistakes

How to use this panel

When not to stop at V = I R

Frequently asked questions

How does this Ohm's law calculator work?

What is the power twin?

What is the decade load ladder?

When is Ohm's law valid?

Why can I not divide by zero?

Is this safe for mains or PCB design?

How is this different from Newton's law or density?

Sources

Close the V = I R triad

Power twin beside Ohm

Decade load ladder

Milli / base / kilo chips

What the panel actually computes

Where this hands off

Worked scenarios

Common mistakes

How to use this panel

When not to stop at V = I R

Frequently asked questions

How does this Ohm's law calculator work?

What is the power twin?

What is the decade load ladder?

When is Ohm's law valid?

Why can I not divide by zero?

Is this safe for mains or PCB design?

How is this different from Newton's law or density?

Sources

What this number means

Share your calculation