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Electrical calculator

Energy Cost Calculator

Estimate electricity usage cost from watts/hours or kWh and your unit rate. Supports custom billing periods; standing charges and taxes are excluded. Runs locally in your browser.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance
Input interpretation
Enter values to calculate.
Result
—
Assurance
Engineering
Declared partition coverage
PASS · 3/3 declared partitions (watts, kwh, invalid-domain) · Matrix
Known limitations
  • Flat unit rate only; no standing/fee (see electricity bill)
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
Usage cost in currency units from watts × hours × days × rate, or from kWh × rate.
Scope
Constant average power over the period
Verification
Engine tested · Source checked · v1.4.2 · CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance· View Manifest · CVP overview · Specification
Versions
Calculation 1.4.2 · CVP protocol 1.0.0-proposed · Evidence 2026-09-13.ssr-dollar-literal
Verification revision
2026-09-13.ssr-dollar-literal · 5/5 property · digest b2d8bb7116f1
Legacy regression
28/28 tests · Production surface contract 4/4
Trust layers
Verification VERIFIED · Production CURRENT · overall VERIFIED
Reference
O1 model · O2 expected_values · O2 numerical_behavior
Interfaces
PASS · UI (SSR) / REST / MCP — ui-ssr is query-result HTML, not a live browser session. Public share URLs use UI ids (powerInput/hoursInput/daysInput/kwhInput/rateInput). CVP-IFACE includes those serialized queries, not only canonical engine keys.
Supplemental domain review
Internal · Pass · electrical-engineer
Named expert review
Not performed
CVP suite
2/2 golden · 12/12 CVP boundary · 21/21 invalid · 5/5 property · 3/3 cross-interface · 4/4 CVP contract · Manifest
Sources
Sources
Evidence
10 legacy golden · 13 legacy boundary · legacy regression suite · 2/2 oracle-backed golden · 21/21 invalid · Artifact integrity PASS · CalculatorX electrical review
This calculator CURRENT · Public schema 1.4.2 matches · Semantic contract ✓ · Production attested · Public/cache ✓ · Origin ✓
Semantic contract
PASS
Full verification

Manifest identity, reference classes, interfaces, suite, and production records.

Formulas

Core equations used by this calculator.

Cost from energyCost = kWh × rate
Cost from wattsCost = (W × h × days ÷ 1000) × rate
Daily costCost/day = (W × h/day ÷ 1000) × rate
Energy and powerE = P × t · P = E / t
iCurrency is shown as $ — enter your local numeric rate per kWh. Convert ¢/kWh or p/kWh by dividing by 100. Standing charges and taxes are not included; use the electricity bill calculator for full-bill estimates. Yearly ≈ daily × 365.

How to use

1

Choose From watts or From kWh

Use watts when you know appliance power and run time; use kWh when you already have energy from a meter or bill.

2

Enter power, hours, days (or kWh) and rate

For a month-style estimate use 30 days; for a year use 365. Rate is your unit price per kWh.

3

Read usage cost

Result updates as you type. Watts mode also shows daily and rough yearly cost.

Example calculations

Common configurations with formula and result.

ϟ

Space heater — monthly

1500 W · 8 h/day · 30 days · $0.20/kWh

1500×8×30/1000 × 0.20
$72.00
ϟ

LED vs incandescent

9 W vs 75 W · 5 h/day · 365 days · $0.15/kWh

W×5×365/1000 × 0.15
~$2.46 vs ~$20.53 / year
ϟ

From bill kWh

120 kWh · $0.15/kWh

120 × 0.15
$18.00
ϟ

Annual estimate

1000 W · 10 h/day · $0.28/kWh

10 kWh/day × 0.28 × 365
~$1022 / year

Typical appliance wattage (approximate ranges)

Common values at a glance.

ApplianceTypical W
LED light bulb3–25
Incandescent bulb15–200
Laptop35–150
Desktop PC100–250
Television25–500
Refrigerator500–1000 (cycles)
Microwave750–1500
Dishwasher1200–2000
Clothes dryer1800–5000
Portable heater750–2000
Window AC1500–5000
EV charger1500–20000
i Nameplate watts are often maximum. Cycling loads use less energy than W_max × clock hours.

Energy Cost calculator specification

Version 1.4.2 · Engine tested · Supplemental domain review · Internal · 2026-09-13

Calculation status

Review policy · Evidence · Reviewed by CalculatorX electrical review (electrical-engineer)

Definition
You pay for energy in kilowatt-hours (kWh), not watts alone. Cost = kWh × rate. From wattage: kWh = W × hours × days ÷ 1000, then multiply by your unit price. This tool estimates usage cost for one device — it does not add standing charges, taxes, or tiered rates.
What it calculates
Usage cost in currency units from watts × hours × days × rate, or from kWh × rate.
Inputs
  • Power (W), hours/day, days, and rate — or energy (kWh) and rate
Outputs
  • Usage cost
  • kWh used (watts mode)
  • Daily and yearly estimates (watts mode)
Formula
Cost = (W × h × days ÷ 1000) × rate; or Cost = kWh × rate
Assumptions
  • Constant average power over the period
  • Single flat unit rate
Units
  • W, h, d, $/kWh → $
Boundary conditions
  • Standing charge and tax not included — usage cost only
  • Missing rate / W / hours / days / kWh → MISSING_REQUIRED_INPUT; rate / W / hours / days / kWh < 0 → VALUE_MUST_BE_NON_NEGATIVE
  • hours > 24 in watts mode → HOURS_PER_DAY_OUT_OF_RANGE
  • Bad mode → INVALID_MODE; non-finite → INVALID_NUMBER
  • Zero W / hours / days / kWh / rate → 0 cost — soft boundary
  • mode=watts uses W×hours×days/1000×rate; mode=kwh uses kWh×rate
Example
1000 W × 4 h/day × 30 days × $0.15/kWh = $18
Validation cases

24 published on this page · 28/28 tests · Production surface contract 4/4 · View evidence

  • 1000 W, 4 h/day, 30 d, $0.15/kWh → $18.00
  • 120 kWh, $0.15/kWh → $18.00
  • 2000 W, 4 h/day, 30 d, $0.15/kWh (2× W) → $36.00 (linear in W)
  • 1000 W, 4 h/day, 30 d, $0.30/kWh (2× rate) → $36.00 (linear in rate)
  • 0 W, 4 h/day, 30 d, $0.15/kWh → $0.00
  • 1000 W, 4 h/day, 0 d, $0.15/kWh → $0.00
  • 1000 W, 4 h/day, 30 d, $0/kWh → $0.00
  • 500 W, 2 h/day, 30 d, $0.20/kWh → $6.00
  • 0 kWh, $0.15/kWh → $0.00
  • 2000 W, 8 h/day, 30 d, $0.12/kWh → $57.60
  • 1500 W, 6 h/day, 1 d, $0.25/kWh → $2.25
  • watts path 1000×4×30@$0.15 equals kWh path 120@$0.15 → both $18.00
  • missing rate → error MISSING_REQUIRED_INPUT
  • mode=joules → error INVALID_MODE
  • rate=-1 → error VALUE_MUST_BE_NON_NEGATIVE
  • W=-1000, 4 h/day, 30 d, $0.15/kWh → error VALUE_MUST_BE_NON_NEGATIVE
  • 1000 W, hours=-4, 30 d, $0.15/kWh → error VALUE_MUST_BE_NON_NEGATIVE
  • 1000 W, hours=25, 30 d, $0.15/kWh → error HOURS_PER_DAY_OUT_OF_RANGE
  • 1000 W, 4 h/day, days=-30, $0.15/kWh → error VALUE_MUST_BE_NON_NEGATIVE
  • kWh=-10, $0.15/kWh → error VALUE_MUST_BE_NON_NEGATIVE
  • watts mode missing W → error MISSING_REQUIRED_INPUT
  • watts mode missing hours → error MISSING_REQUIRED_INPUT
  • watts mode missing days → error MISSING_REQUIRED_INPUT
  • kwh mode missing kWh → error MISSING_REQUIRED_INPUT
Sources
Last reviewed
2026-09-13
Reviewed by
CalculatorX electrical review (electrical-engineer)
Calculation version
1.4.2

Background

Interpretation and common distinctions.

Estimate how much an appliance costs to run from wattage and usage time, or from kilowatt-hours you already know. Enter your local unit rate (the numeric $/kWh, €/kWh, or £/kWh from your bill). Results are usage cost only — no standing charge or tax.

Supported and not supported

Supported

  • Watts mode: Cost = (W × h × days / 1000) × rate
  • kWh mode: Cost = kWh × rate
  • Soft zeros for zero load/hours/days/kWh/rate
  • API capability electrical.energy_cost · pin calculation_version: 1.4.2

Not supported

  • Standing charge, tax, or tiered TOU bands
  • Full bill composition (use Electricity bill calculator)

Stable errors: MISSING_REQUIRED_INPUT, INVALID_NUMBER, INVALID_MODE, VALUE_MUST_BE_NON_NEGATIVE, HOURS_PER_DAY_OUT_OF_RANGE.

Modes

Tab Inputs Use when
From watts Power (W), hours/day, days, rate Nameplate or typical wattage + how long it runs
From kWh Energy (kWh), rate Meter reading, bill block, or known consumption

How the calculation works

  1. Energy (kWh) — From watts: E = W × h × days / 1000. From a known total: enter kWh directly.
  2. Cost — Cost = E × rate.
  3. Daily / yearly (watts mode) — Daily cost uses one day’s energy; the result panel also shows a rough yearly figure as daily × 365.

Example (watts): 1000 W × 4 h/day × 30 days × 0.15/kWh → 120 kWh → 18.00. Daily ≈ 0.60; yearly ≈219.

Example (kWh): 120 kWh × 0.15 → 18.00.

For energy only (no money), use the energy consumption calculator. For bill-style totals with standing charge and other fees, use the electricity calculator.

Units of electricity (quick reference)

Unit Role Note
W / kW Power Rate of energy use; 1 kW = 1000 W
kWh Energy What you usually pay for; 1 kW for 1 hour
BTU/h Power (heat) ~0.293 W per BTU/h; AC often labeled in BTU
hp (metric) Power ≈ 735.5 W
ton (refrigeration) Power ≈ 3517 W ≈ 12,000 BTU/h

Convert exotic power units to watts, then use From watts.

Tips for better estimates

  • Match hours/day to real use (not 24 h unless it truly runs continuously).
  • For cycling loads (fridge, HVAC), prefer a measured kWh or a lower effective wattage — max label × time overstates cost.
  • Use days = 30 for a month-style estimate, 365 for a year, or your exact billing period length.
  • Rate from the bill: if you see 15 ¢/kWh or 26 p/kWh, enter 0.15 or 0.26.

Energy-saving ideas (high impact)

  1. Track which devices run long hours; cut standby and idle loads.
  2. Replace remaining incandescent bulbs with LEDs.
  3. Set back heating/cooling when away; seal drafts and improve insulation.
  4. Prefer efficient appliances when replacing high-use equipment (dryer, fridge, HVAC).

Other calculators in this family: Amps to kW Calculator, Amps to VA Calculator, Amps to Volts Calculator, Electric Power Calculator, Energy Consumption Calculator, eV to Volts Calculator, kVA to Amps Calculator, kVA to kW Calculator . Explore all Power & Energy.

→ Amps to kW Calculator Convert amps and volts to real power in kW for DC, AC single-phase, and balanced AC three-phase line-to-line. Runs locally in your browser. Free online tool — no sign-up. › → Amps to VA Calculator Convert amps and volts to apparent power in VA or kVA for single-phase and three-phase circuits. Also convert VA back to amps. Fast and free. › → Amps to Volts Calculator Solve voltage from current and resistance or power using Ohm’s law and P = V × I. Supports resistive DC and RMS AC estimates with clear formulas. › → Electric Power Calculator Calculate electrical power in watts from voltage and current for DC, single-phase AC, or balanced three-phase AC, from current and resistance, or from energy over time. › → Energy Consumption Calculator Estimate energy use in kWh from device watts and hours of operation. Useful for appliance and load planning. Runs locally in your browser. Try it free. › → eV to Volts Calculator Relate electronvolt energy to electric potential difference through ΔE = qΔV. eV and volts measure different physical quantities. Runs locally in your browser. › → kVA to Amps Calculator Convert kVA and voltage to line current for single-phase and three-phase systems. Uses √3 for three-phase line-to-line volts. Runs locally in your browser. › → kVA to kW Calculator Convert apparent power (kVA) to real power (kW) with power factor. States when PF is required and when loads are assumed balanced. Try it free. ›
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Frequently asked questions

Key distinctions behind the calculation.

How do I estimate electricity costs for an appliance?

Find wattage, estimate hours used per day, pick a period (e.g. 30 days), and multiply energy in kWh by your rate. Or enter total kWh if you already have it from a meter or bill.

Does this include standing charges and taxes?

No. Results are energy × unit rate only. Fixed daily standing charges, VAT/sales tax, and connection fees need a full bill calculator or your supplier’s tariff sheet.

What rate should I enter?

Use the unit price from your electricity bill ($/kWh, €/kWh, or £/kWh — the $ label is currency-agnostic). For tiered or time-of-use plans, pick the band that applies to that usage.

Why is nameplate wattage higher than real use?

Labels often show maximum power. Refrigerators, HVAC, and washers cycle on and off; typical energy is lower than W_max × time. Adjust hours or use a measured kWh when possible.

Watts, kW, BTU, and horsepower?

Enter watts here (kW × 1000). Rough conversions — 1 ton refrigeration ≈ 3517 W ≈ 12,000 BTU/h; 1 metric hp ≈ 735.5 W; 1 mechanical hp ≈ 745.7 W. Convert to watts first, then run the cost calc.

How can I reduce electricity costs?

Cut run hours, replace inefficient loads (e.g. LED vs incandescent), improve heating/cooling setbacks and insulation, and choose efficient appliances — small wattage changes add up over many hours.