Electrical, Battery Backup & Generator Sizing Calculators
Calculate UPS battery runtime hours, circuit amperage, and backup generator wattage using published equations, explicit efficiency factors, and National Electrical Code (NEC) continuous-load margins.
Live Interactive Calculators
Select a tool below to run interactive calculations with transparent equations, NEC continuous-load margins, and instant results.
E_daily = P × t × DF × Q | E_monthly = (E_daily × 30) ÷ 1,000 | Cost = E_monthly × RateElectricity Usage Calculator
Calculate daily and monthly electricity usage in Watt-hours and kilowatt-hours across household appliances with duty cycles and utility cost estimates.
- •Appliance energy consumption in daily/monthly Wh and kWh
- •Multi-appliance inventory total with visual consumption share
- •Compressor and thermostatic duty cycle scaling (10% to 100%)
- •Estimated monthly electricity utility charge based on local rate
Wh = V × Ah | Wh_usable = Wh × DoD | Ah_req = (P × t) ÷ (V × η × DoD)Battery Capacity & Sizing Calculator
Calculate battery storage in Watt-hours (Wh) and Amp-hours (Ah). Evaluate usable capacity across LiFePO4 and lead-acid chemistries, or size battery banks and unit counts for target loads.
- •Nominal and usable energy in Wh and kWh
- •Depth of discharge (DoD) benchmarks for LiFePO4, AGM, and NMC
- •Series vs. parallel bank voltage and capacity calculations
- •Appliance load sizing with inverter efficiency derating
Peak = Running W + Max(Starting Surge W)Generator Size Calculator
Calculate running watts, single-motor peak starting demand, and 1.25x recommended generator capacity for home outage backup, RV air conditioners, and jobsite equipment.
- •Total running watts and highest motor surge delta
- •Peak starting demand and 1.25x planning capacity
- •Apparent power (kVA) at configurable power factor
- •21 residential, RV, and jobsite appliance presets
T = (V × Ah × DoD × η) ÷ WUPS & Battery Backup Runtime Calculator
Estimate how long a 12V, 24V, or 48V battery bank or UPS will sustain continuous AC loads while accounting for inverter efficiency, usable depth of discharge, and high discharge C-rates.
- •Runtime in hours and minutes
- •Usable battery energy (Wh) and DC current draw (A)
- •LiFePO4 (90% DoD), AGM/Gel (50% DoD), and NMC presets
- •1.25x continuous inverter sizing margin
Total Bill = (kWh × Rate) + Fixed + Riders + Tax | Effective = Bill ÷ kWhElectricity Cost & Bill Calculator
Calculate monthly electric utility charges from volumetric kWh usage, tiered electric rates, fixed customer fees, and taxes to reveal true effective cost per kWh.
- •Monthly and annual electric utility bill estimate
- •Effective cost per kWh across all charges
- •Volumetric energy supply vs fixed delivery breakdown
- •Tiered rate schedules and seasonal rate comparison
I = P ÷ (V × PF) | 3Φ: I = P ÷ (√3 × V × PF)Watts to Amps Calculator
Convert active power (Watts) to electrical current (Amps) across DC, single-phase AC (120V/240V), and balanced three-phase AC (208V/240V/480V) circuits with power factor adjustments.
- •Operating current (Amps) and apparent power (VA)
- •NEC 125% continuous-load minimum breaker amps
- •Standard NEC 240.6(A) breaker trade size match
- •Line-to-Line vs. Line-to-Neutral 3-phase support
P = I × V × PF | 3Φ: P = √3 × V × I × PFAmps to Watts Calculator
Convert electrical current (Amps) and voltage to real power (Watts) and apparent power (VA) across DC, single-phase 120V/240V, and balanced 3-phase circuits.
- •Real power (Watts) and apparent power (VA)
- •NEC continuous-load benchmark (80% for 3+ hr duty on standard breakers)
- •Standard 15A & 20A household circuit capacity benchmarks
- •DC, single-phase AC, and three-phase AC configurations
I_nominal = P_array ÷ V_battery | Voc_cold = Voc_STC × [1 + α × (T_min - 25°C)]Solar Charge Controller Calculator
Calculate the required charge controller amperage rating and verify cold-temperature open-circuit voltage headroom across MPPT and PWM technologies.
- •Nominal and planning charging current (Amps)
- •Standard controller current rating class recommendation
- •Cold-weather Voc expansion check (NEC 690.7)
- •12V, 24V, and 48V DC battery system voltage support
E_nom = (E_daily × N_days) ÷ (η_inv × DoD) | Ah = E_nom ÷ V_dcSolar Battery Calculator
Size off-grid and backup solar battery banks in kWh and Amp-hours based on daily energy consumption, days of autonomy, inverter losses, and usable depth of discharge.
- •Nominal storage capacity in kWh and Watt-hours
- •Battery-bank Amp-hours at 12V, 24V, and 48V DC bus
- •Load-side autonomy energy and inverter delivery energy
- •Simplified solar PV array replenishment wattage estimate
P_array_kW = (E_daily × Offset%) ÷ (PSH × PR) | Panels = Math.ceil(P_array_W ÷ W_panel)Solar System Size Calculator
Calculate the residential solar system size in kW and approximate panel count required to offset monthly electricity usage based on local peak sun hours.
- •Estimated system size (kW DC) and panel count
- •Daily and annual solar energy generation targets
- •Net module area and gross roof space with fire setbacks
- •Module wattage comparison across 330W to 450W panels
VD = mult × I × (L ÷ 1,000) × R | 1Φ: 2 | 3Φ: √3Voltage Drop Calculator
Calculate circuit voltage drop, percentage loss, and receiving terminal voltage across DC, single-phase AC, and balanced three-phase AC systems.
- •Calculated voltage loss (Volts) and drop percentage (%)
- •Receiving terminal voltage at connected load
- •Total circuit loop resistance (75°C stranded baseline)
- •Adjacent AWG & kcmil conductor comparison table
Gallons/hr = Max Fuel / HoursGenerator Fuel Consumption Calculator
Estimate how much gasoline, propane, or diesel your generator will consume based on its running wattage and fuel tank size.
- •Hourly fuel consumption rate
- •Cost per 24 hours of operation
- •Total fuel tank runtime
- •Gasoline, Propane, and Diesel presets
P = √3 × V_LL × I × PF | S = √3 × V_LL × I | I = P ÷ (√3 × V_LL × PF)Three Phase Power Calculator
Calculate 3-phase real power (kW), apparent power (kVA), reactive power (kVAR), and line current (Amps) across balanced commercial and industrial circuits.
- •Real active power (kW) and apparent demand (kVA)
- •Line current (Amps) solved bidirectionally from load power
- •Line-to-line (V_LL) and line-to-neutral (V_LN) conversion
- •Power triangle decomposition (kW, kVA, and kVAR)
θ_roof = atan(pitch/12) × (180/π) | Tilt_winter = lat + 15°Solar Panel Tilt Angle Calculator
Calculate optimal solar panel tilt angles, compass orientation, and roof pitch differences for your latitude across year-round, winter, and summer optimization targets.
- •Optimal tilt angle and empirical Landau estimate (25° to 50° N)
- •Roof pitch slope conversion (0/12 to 12/12) and geometric delta
- •True South (180°) and True North (0°) compass azimuth guidance
- •Low-tilt rainwater drainage and cold-climate snow shedding advisories
Practical Engineering Guides & Outage Planning
In-depth technical guides explaining calculations, safety codes, and equipment selection with worked examples.
What Size Generator Do I Need to Run My House? (Complete Calculation Guide)
Learn how to calculate required continuous running wattage and motor startup surge demand for your home during utility outages. This comprehensive engineering resource walks through real-world electrical equipment, inrush currents, power transfer methods, and NEC continuous-load margins.
Running Watts + Max Starting Surge Delta + 25% Planning Margin.
Step-by-step 5.1 kW winter essentials outage model with furnace and fridge.
- •1-click bridge to load the 5.1 kW storm scenario directly into the calculator
- •Transfer switch safety vs. illegal backfeeding guidelines (NEC Article 702)
- •Inverter vs. open-frame vs. standby generator comparison table
How Long Will a 100Ah Battery Last? 12V Appliance Runtime Guide
Realistic delivered runtime estimates for refrigerators, CPAP machines, laptops, TVs, and inverters across LiFePO4 and lead-acid deep-cycle batteries.
What Size Generator Do I Need to Run a Refrigerator?
Determine exact running watts and compressor startup surge requirements for residential kitchen refrigerators, garage freezers, and extension cord AWG safety.
What Does Ah Mean on a Battery? Amp-Hours Explained
Understand battery charge capacity, convert Amp-hours to Watt-hours (Wh), and evaluate how chemistry, depth of discharge, and Peukert losses determine runtime.
What Is a Watt-Hour (Wh)? Watts vs. Watt-Hours Explained
Discover the difference between instantaneous power (Watts) and energy consumed over time (Watt-hours), with practical battery runtime and utility calculations.
Browse Calculators & Sizing Guides by Power Cluster
Immediate 1-hop access to all 14 interactive calculators and 8 standalone engineering sizing guides.
Solar PV & Storage
Array sizing, tilt & charge time
Generators & Outage
Wattage, fuel rate & home backup
Battery & UPS Storage
Capacity, runtime & inverter size
Circuits & Electricity
Amps, watts, voltage drop & cost
Essential Sizing Guides & Reference Schematics
Worked engineering sizing methodologies, calculation benchmarks, and downloadable quick-reference diagrams.
Solar Panels Series vs Parallel: Complete Wiring Guide & Printable Schematics
Understand how series, parallel, and series-parallel strings determine array voltage, operating current, and charge controller compatibility. Download our verified two-page US Letter engineering reference schematic for your workbench or jobsite binder.
How Much Energy Does a Solar Panel Produce? (400W Examples)
Learn daily, monthly, and annual solar panel electricity generation. Explore 400W reference benchmarks, regional peak sun hours, and realistic system deratings.
How Long Does It Take to Charge a Battery with Solar Panels?
Calculate realistic battery recharge hours across 12V, 24V, and 48V banks. Model solar panel wattage, controller efficiency, effective solar irradiance, and chemistry-specific charging factors.
How Many Amp Hours Do I Need for a Battery Bank?
Calculate total battery bank amp-hours from daily appliance Watt-hours, nominal voltage (12V, 24V, 48V), autonomy days, usable depth of discharge, and inverter efficiency.
How CalcMyPower Models Electrical & Power Loads
Every CalcMyPower calculator displays its governing mathematical formula and transparent baseline parameters. We clearly identify where 1.25x planning margins reflect National Electrical Code (NEC Article 210/430) continuous-load rules versus practical equipment surge headroom.
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