Does this handle discharge?

Not directly. Use Vc(t) = V0 × e^(−t/RC) for discharge scenarios.

What is the time constant?

τ = R × C. At 1τ, voltage is about 63% of supply; at 5τ it’s effectively fully charged.

Do I need to convert units?

Keep R in ohms, C in farads, and time in seconds. Microfarads must be converted to farads (e.g., 100 µF = 0.0001 F).

How accurate is this vs. real circuits?

Real components have ESR/leakage and load effects. This is an ideal model for quick estimates.

Can I model a different final voltage?

Yes—set supply voltage to your final target. For discharge, use the exponential decay formula instead.

science calculator

Capacitor Charge Calculator

Compute capacitor voltage and charge at any point during RC charging.

Results

Capacitor voltage (V): 3.16
Charge (C): 0.00

How to use this calculator

Enter supply voltage, resistance, capacitance, and elapsed time.
We calculate capacitor voltage and charge at that time using the RC charge equation.
Use the outputs to design timing circuits or estimate charge level.

Inputs explained

Supply voltage: Voltage source charging the capacitor.
Resistance: Series resistance that sets the RC time constant.
Capacitance: Capacitor value in farads.
Time since start: Seconds elapsed since charging began.

How it works

We apply Vc(t) = V(1 − e^(−t/RC)). Charge = C × Vc.

Formula

Vc(t) = V(1 − e^(−t / RC))
Q(t) = C × Vc(t)

When to use it

Sizing RC delays for LEDs, relays, or debounce circuits.
Estimating voltage mid-charge for ADC sampling.
Teaching or checking RC exponential math without manual calculation.

Tips & cautions

Time constant τ = R × C. At 1τ the capacitor is ~63% charged; ~5τ is >99%.
Keep units consistent (ohms, farads, seconds) to avoid scaling errors.
For discharge, use Vc(t) = V0 × e^(−t/RC); this tool focuses on charging.
Ideal RC only—ignores ESR, leakage, and source/load effects.
Assumes a step input and no load on the capacitor during charge.
Single-stage RC; complex networks need circuit simulation.

Worked examples

5 V supply, 1 kΩ, 1 mF at 1 second

Vc ≈ 4.33 V
Charge ≈ 0.0043 C

Time constant

t = RC (1 s) gives Vc ≈ 63% of supply voltage.

Deep dive

This capacitor charge calculator applies Vc(t)=V(1−e^(−t/RC)) to show capacitor voltage and charge at any time. Enter supply voltage, resistance, capacitance, and elapsed seconds for instant RC math.

Use it for timing circuits, lab work, or sanity checks. It assumes an ideal RC; real parts have ESR and leakage that slightly change the curve.

FAQs

Does this handle discharge?: Not directly. Use Vc(t) = V0 × e^(−t/RC) for discharge scenarios.
What is the time constant?: τ = R × C. At 1τ, voltage is about 63% of supply; at 5τ it’s effectively fully charged.
Do I need to convert units?: Keep R in ohms, C in farads, and time in seconds. Microfarads must be converted to farads (e.g., 100 µF = 0.0001 F).
How accurate is this vs. real circuits?: Real components have ESR/leakage and load effects. This is an ideal model for quick estimates.
Can I model a different final voltage?: Yes—set supply voltage to your final target. For discharge, use the exponential decay formula instead.

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