Calculate electricity consumption in kilowatt-hours and total cost. Enter wattage, hours of use per day, and your electricity rate.
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A DIY homeowner in Ohio is building a 16×20 ft pressure-treated pine deck. Wants to calculate board footage, joist spacing requirements, and total material cost before going to the lumber yard.
Takeaway: Lumber prices fluctuate 30-50% based on housing market cycles — 2026 prices are down from 2021 peaks. Add 10% waste factor to board counts for cuts and defects. Composite decking (Trex, etc.) costs 2-3× more but eliminates annual staining.
Lumber calculations typically add 10-15% for cuts and defects. Tile installations in rooms with obstacles (cabinets, islands) need 15-20% extra. Straight-line flooring installations need 5-10%. Applying a flat waste factor to all project types leads to significant under- or over-ordering.
Calculators for beam sizing, deck load, and structural spans provide estimates only. Actual structural work (load-bearing wall removal, deck ledger attachment, header sizing) requires permits and often a licensed engineer's stamp. Using undersized members based on a web calculator without engineer review creates safety and liability risk.
Wire gauge calculators for circuit sizing assume straight runs. Every 90-degree bend, junction box, and conduit fill fraction introduces derating factors. The NEC (National Electrical Code) derate rules for conductors in conduit, ambient temperature, and bundled cables can require upsizing by 1-2 wire gauges beyond the basic ampacity calculation.
Joist span tables, snow load requirements, and stud spacing rules vary by jurisdiction. A 2×10 joist spanning 14 feet may pass in a low-snow-load area and fail in a high-alpine zone. Always cross-reference with your local building department's adopted code edition (IBC, IRC) before finalizing material specifications.
Based on your inputs
$33.60 total cost
| Daily Consumption | 8.000 kWh/day |
|---|---|
| Total over 30 days | 240.00 kWh |
| Daily Cost | $1.120 |
| Total Cost | $33.60 |
Analyze 3+ calcs to unlock your Financial Picture dashboard (cross-analysis of all your numbers).
Your electricity bill is based on kilowatt-hours (kWh) consumed. Understanding how to calculate kWh lets you estimate the cost of running any appliance and find opportunities to reduce your energy bill.
kWh = (Watts x Hours of use) / 1,000
Cost = kWh x Rate per kWh
Example: A 1,500W space heater running 8 hours per day for 30 days:
kWh = (1,500 x 8) / 1,000 = 12 kWh per day
Monthly: 12 x 30 = 360 kWh
Cost at $0.14/kWh: 360 x $0.14 = $50.40 per month
LED light bulb (10W, 8 hrs/day): $0.34/month
Laptop (65W, 8 hrs/day): $2.18/month
Desktop computer (300W, 8 hrs/day): $10.08/month
Refrigerator (150W, 24 hrs/day): $15.12/month
Window AC (1,000W, 8 hrs/day): $33.60/month
Space heater (1,500W, 8 hrs/day): $50.40/month
Electric dryer (5,000W, 1 hr/day): $21.00/month
EV charger (7,200W, 3 hrs/day): $90.72/month
Electricity rates vary significantly by state (2024 averages):
Cheapest: Louisiana $0.094 | Idaho $0.095 | Utah $0.098
Average: Texas $0.128 | Florida $0.137 | Ohio $0.140
Most expensive: Connecticut $0.249 | Massachusetts $0.271 | Hawaii $0.319
Your bill shows kWh consumed during the billing period. Divide by the number of days to get daily consumption. The average US household uses about 29 kWh/day (886 kWh/month). Use our kWh calculator to project costs for specific appliances and understand your electricity bill.
The biggest energy hogs in your home are heating, cooling, and hot water systems. Knowing the exact electricity consumption of each appliance helps you target the most impactful energy savings.
Space heater (1,500W): 1.5 kWh/hour = $5.04/day at 8 hrs
Electric baseboard (1,000W per 4-ft section): 1.0 kWh/hour per section
Heat pump (3,500W): 3.5 kWh/hour (but heats 2-3x more efficiently than resistive)
Electric furnace (10,000-20,000W): 10-20 kWh/hour when running
Ceiling fan (75W): 0.075 kWh/hour = $0.25/day at 24 hrs
Window AC 5,000 BTU (500W): 0.5 kWh/hour = $1.68/day at 8 hrs
Window AC 10,000 BTU (1,000W): 1.0 kWh/hour = $3.36/day at 8 hrs
Central AC (3,500W): 3.5 kWh/hour = $11.76/day at 8 hrs
Portable AC (1,200W): 1.2 kWh/hour = $4.03/day at 8 hrs
Refrigerator (150W average): 3.6 kWh/day = $15.12/month
Electric oven (2,500W): 2.5 kWh/hour of active cooking
Microwave (1,000W): 0.1 kWh per 6-minute use
Dishwasher (1,800W): 1.8 kWh per cycle
Coffee maker (900W): 0.15 kWh per brew cycle
LED TV 55" (80W): 0.08 kWh/hour = $2.69/month at 8 hrs/day
Gaming console (200W active, 10W standby): 0.2 kWh/hour active
Wi-Fi router (10W, always on): 0.24 kWh/day = $1.01/month
Phone charger (5W): negligible -- about $0.02/month
Devices in standby mode (phantom load) consume 5-10% of total household energy. A typical home wastes $100-$200/year on standby power. The worst offenders: cable boxes (15-30W), game consoles (10-25W), and older TVs (5-15W).
Calculate costs for your specific appliances with our kWh calculator. For solar panel sizing and payback, see our solar panel calculator.
Charging an electric vehicle at home is significantly cheaper than gasoline, but the exact cost depends on your electricity rate, EV efficiency, and charging equipment. This guide helps you calculate your specific EV charging costs.
Cost per charge = Battery capacity (kWh) x Electricity rate ($/kWh)
Cost per mile = Cost per charge / Range per charge
Tesla Model 3 (60 kWh battery, 270-mile range):
Full charge cost: 60 x $0.14 = $8.40
Cost per mile: $0.031
Monthly (1,000 miles): $31.00
Tesla Model Y (75 kWh, 310-mile range):
Full charge: $10.50 | Per mile: $0.034 | Monthly: $33.87
Chevrolet Bolt (65 kWh, 259-mile range):
Full charge: $9.10 | Per mile: $0.035 | Monthly: $35.14
Ford F-150 Lightning (131 kWh, 300-mile range):
Full charge: $18.34 | Per mile: $0.061 | Monthly: $61.13
At $3.50/gallon and 30 MPG: gasoline costs $0.117/mile
At $0.14/kWh and 3.5 miles/kWh: electricity costs $0.040/mile
Savings: 66% cheaper to drive electric
For 12,000 miles/year: Gas = $1,400/year, Electric = $480/year. Annual savings: $920.
Level 1 (standard 120V outlet): 1.4 kW, adds 3-5 miles/hour. Fine for PHEVs or short commutes.
Level 2 (240V dedicated circuit): 7.2-9.6 kW, adds 25-35 miles/hour. Charges overnight.
A Level 2 charger draws 30-40 amps on a 240V circuit. Consult an electrician to verify your panel can handle this load. Then use our kWh calculator to project monthly charging costs at your specific electricity rate.
A kWh is a unit of energy equal to using 1,000 watts for 1 hour. It's what your electric meter measures and what your utility charges per unit.
kWh = (Watts × Hours per day) ÷ 1000. Then multiply by days for total consumption.
The US average is about $0.13–0.17 per kWh as of 2024. Rates vary by state from $0.09 (Louisiana) to $0.29+ (Hawaii).
The average US home uses about 886 kWh per month (about 29 kWh/day) according to the EIA.
Switch to LED bulbs, upgrade to Energy Star appliances, seal air leaks, and adjust your thermostat by a few degrees. Using a programmable thermostat alone can save 10-15% on heating and cooling costs annually.
A kilowatt (kW) measures power, the rate of energy use at a given moment. A kilowatt-hour (kWh) measures total energy consumed over time. Running a 1 kW device for 2 hours uses 2 kWh of energy.
Note the meter reading at the start and end of a period. Subtract the earlier reading from the later one to find total kWh consumed. Digital meters display the number directly, while analog meters require reading each dial.
First convert amps to watts by multiplying amps by voltage. Then use the kWh formula: kWh = (amps x volts x hours) / 1000. A 10-amp device on a 120V circuit running 5 hours uses 6 kWh.
Time-of-use pricing charges different rates depending on the time of day. Peak hours cost more, while off-peak hours are cheaper. Shifting heavy energy use like laundry and EV charging to off-peak hours can significantly reduce your bill.
Your bill lists total kWh consumed during the billing period. Divide by the number of days to get daily usage. Compare against the US average of about 29 kWh per day to see if your consumption is above or below normal.
kWh = (Watts × Hours/day) ÷ 1000
Cost = kWh × Rate ($/kWh)
Every formula on this page traces to a federal agency, central bank, or peer-reviewed institution. We cite the rule-makers, not secondhand blogs.
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Calculations are for educational purposes only. Consult a qualified financial advisor for personalized advice.