Electrical calculator

Watts to Joules Calculator

Convert watts and time to energy in joules (and reverse). Shows W × s = J with worked timing examples. Runs locally in your browser. Try it free.

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Result

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Enter values to calculate.

Inputs—

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Formula—

Trust summary Engine tested · Source checked · 12/12 tests · Production surface contract 4/4 · v1.2.1

Input interpretation: Enter values to calculate.
Result: —
Model: Energy from power and time, or average power from energy and time.
Scope: Constant average power over the interval
Verification: Engine tested · 12/12 tests · Production surface contract 4/4 · Source checked · v1.2.1
Named expert review: Optional · Not performed
Sources: SI definition of the watt — 1 W = 1 J/s
NIST Guide to the SI (SP 811) — Joule and watt as coherent SI units
IEC 60050 — International Electrotechnical Vocabulary — Active power (IEV 131-11-42)
IEC 60050 — International Electrotechnical Vocabulary — Active energy (IEV 131-11-57)
BIPM SI Brochure (9th edition, version 4.01) — Watt as joule per second
Sources
Evidence: 12 golden · Production surface contract 4/4 · Artifact integrity PASS
Production: Embedded snapshot: STALE · Last attested schema matched 1.2.1 snapshot / local build · Semantic contract ✓ · Last attestation PASS · current evidence changed · re-attestation required · Public/cache ✓ · Origin ✓ · Live production status STALE (1 capability; 163 remain CURRENT) @ 2026-09-19T00:00:17.039Z
Semantic contract: PASS

Formulas

Core equations used by this calculator.

Watts → joulesE(J) = P(W) × t(s)

Joules → wattsP(W) = E(J) ÷ t(s)

With minutesE(J) = P(W) × t(min) × 60

With hoursE(J) = P(W) × t(h) × 3600

i1 W = 1 J/s by definition. Enter power in watts (1 kW = 1000 W; 1 mW = 0.001 W). Energy prefixes: 1 kJ = 1000 J; 1 MJ = 10⁶ J. Related billing unit: 1 Wh = 3600 J; 1 kWh = 3.6×10⁶ J.

How to use

Choose direction and time unit

W → J for energy, or J → W for average power. Pick seconds, minutes, or hours.

Enter power (or energy) and time

Convert kW→W and kJ→J before entering if needed.

Read joules or watts

The result updates as you type. For utility bills, joules ÷ 3,600,000 = kWh.

Example calculations

Common configurations with formula and result.

100 W for 60 s

Default check

100 × 60

6000 J

50 W for 25 s

Short interval

50 × 25

1250 J

2 W for 1 hour

Use W → J (h)

2 × 3600

7200 J

100 W bulb for 1 s

Definition of the watt

100 × 1

100 J

Joules → watts

6000 J over 60 s

6000 ÷ 60

100 W

Watts → joules at t = 1 s

Common values at a glance.

Power	Time	Energy
1 W	1 s	1 J
10 W	1 s	10 J
100 W	1 s	100 J
100 W	60 s	6000 J
2 W	1 h	7200 J
1000 W	1 h	3,600,000 J (1 kWh)

i At t = 1 s, joules equal the numeric watt value. Longer time scales energy linearly.

Watts to Joules calculator specification

Version 1.2.1 · Engine tested

Calculation status

Engine tested 12/12 tests · Production surface contract 4/4
Named expert review Not performed
Calculation version 1.2.1

Review policy · Evidence

Definition: A watt is one joule per second (1 W = 1 J/s). Energy in joules is power times time: E(J) = P(W) × t(s). You cannot convert watts to joules without a duration. Reverse: P = E ÷ t. This tool accepts time in seconds, minutes, or hours.
What it calculates: Energy from power and time, or average power from energy and time.
Inputs: Power P (W) and time t (s, min, or h) → joules
Energy E (J) and time t → watts
Outputs: Energy in J, or power in W
Formula: E=P·t; P=E/t (t in seconds after unit conversion)
Assumptions: Constant average power over the interval
Units: W, s → J
Boundary conditions: W→J (product / scale-product): zero P or t → 0 J
J→W (quotient / scale-quotient): t = 0 → 0 W — soft
Zero energy → 0 W on reverse
Minute/hour modes scale time by 60 / 3600 before E = P·t
Example: 100 W × 60 s = 6000 J
Validation cases: 13 published on this page · 12/12 tests · Production surface contract 4/4 · View evidence
100 W, 60 s → 6000 J
50 W, 25 s → 1250 J
2 W, 1 h → 7200 J
100 W, 1 min → 6000 J
6000 J, 60 s → W → 100 W
200 W, 60 s (2× P) → 12000 J (linear in P)
100 W, 120 s (2× t) → 12000 J (linear in t)
0 W, 60 s → 0 J
100 W, 0 s → 0 J
6000 J, 0 s → W → 0 W (soft: zero t → 0)
0 J, 60 s → W → 0 W
100 W → 6000 J → W round-trip at 60 s → 100 W
7200 J, 1 h → W → 2 W
Sources: SI definition of the watt — 1 W = 1 J/s
Supports: E = P × t; P = E / t
NIST Guide to the SI (SP 811) — Joule and watt as coherent SI units
Supports: Energy–power–time relationships; Wh/kWh note
IEC 60050 — International Electrotechnical Vocabulary — Active power (IEV 131-11-42) · accessed 2026-09-05
Supports: P is active power; unit watt (W)
IEC 60050 — International Electrotechnical Vocabulary — Active energy (IEV 131-11-57) · accessed 2026-09-05
Supports: Active energy W = ∫p dt; coherent SI unit joule (J). Distinguishes energy from power
BIPM SI Brochure (9th edition, version 4.01) — Watt as joule per second · 2026-06 · DOI · accessed 2026-09-05
Supports: 1 W = 1 J/s; E = P × t
Calculation version: 1.2.1

Background

Interpretation and common distinctions.

Convert watts (power) and time to joules (energy) — or joules and time back to watts.

E((J)) = P((W)) × t((s)) P((W)) = (E((J)))/(t((s)))

By definition 1 W = 1 J/s. You cannot convert watts to joules without a duration.

Default example: 100 W × 60 s = 6000 J.

Modes

Tab	Formula
W → J (s)	E = P × t
W → J (min)	E = P × tₘᵢₙ × 60
W → J (h)	E = P × tₕ × 3600
J → W (…)	Divide energy by the same time base

Power vs energy

Quantity	Unit	Meaning
Power	watt (W)	How fast energy is delivered
Energy	joule (J)	How much work / heat / electricity was used

A 100 W bulb uses energy at 100 J every second. Run it longer → more joules. Same energy at higher power → shorter time.

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Frequently asked questions

Key distinctions behind the calculation.

How do I convert watts to joules?

Multiply power by time in seconds: E(J) = P(W) × t(s). For minutes multiply by 60; for hours multiply by 3600. Watts alone are not energy — you need a duration.

How do I convert joules to watts?

Divide energy by time: P(W) = E(J) ÷ t(s). That gives the average power over the interval.

What is the difference between watts and joules?

Joules measure energy (work done). Watts measure power (energy per second). 1 W = 1 J/s. Higher power delivers the same energy in less time.

How many watts equal one joule?

Exactly one watt delivers one joule every second. So 1 J over 1 s is 1 W average power — not “1 W = 1 J” without time.

How do joules relate to kWh?

1 Wh = 3600 J. 1 kWh = 3.6×10⁶ J. Divide joules by 3,600,000 to get kilowatt-hours for billing-style energy.

Can I enter kilowatts?

Convert to watts first (×1000), or enter kW as W after scaling. Example: 1.5 kW for 2 h → 1500 W × 7200 s = 10,800,000 J.

Is this the same as volts × coulombs?

Both give joules, but different inputs. E = P×t uses power and time; E = V×Q uses voltage and charge. Use volts to joules for the charge path.