Load list
Running and starting kW by load, plus which loads must start together. Estimates end where a metered load study begins.
Methodology
How GeneratorCalc calculates.
Explicit-input models with visible formulas, dated baselines, machine-checked test cases, and a stated verification boundary. Screening-grade arithmetic for backup-power planning, not engineering design.
The principle
Every result must be reproducible from the inputs on the page.
Each calculator is a fixed formula over labeled inputs. There are no hidden scores, no black-box adjustments, and no location lookups: the numbers you type, plus the stated defaults, fully determine the outputs. Every calculator page shows its formula, and every calculator ships with automated test cases that fixed inputs must reproduce before publication.
Units and conventions
One consistent system across all seventy-two tools.
Power, energy, and fuel
kW measures rate of use; kWh measures accumulated use. Fuel use derives from loaded kW over run hours against the manufacturer fuel table, interpolated between load points, never from kW alone.
Money handling
Fuel prices and service rates are entered in local currency and converted once, at a single documented step. Displayed money rounds to cents; intermediate values keep full precision so chained steps do not drift.
Duty and ratings
Standby (ESP), prime (PRP), and continuous (COP) ratings follow ISO 8528. Where duty is uncertain, the input stays editable and the assumption stays labeled, rather than being buried in a fixed factor.
Precision statement
Outputs are screening-grade: good enough to rank options, size a first pass, or check a quote. They are not commissioning tests and do not replace load-bank testing, short-circuit studies, or installer verification.
Method by category
What each tool family models, and what it assumes.
Load lists
Connected and running loads sum nameplate kW with starting multiples for the largest motor. Estimates assume the duty input states steady or cycling operation explicitly.
Sizing and derating
Required kW and kVA derive from running load plus starting surge, a growth margin, and the ISO 8528 duty rating. Altitude and ambient temperature derate every rating before the nameplate is chosen.
Fuel and runtime
Consumption interpolates the manufacturer fuel table at the expected load factor; runtime divides usable fuel by that rate. Tank usable fraction and reserve policy stay visible inputs.
Installation
Pad, transfer switch, fuel storage, ventilation, exhaust, and permitting line items follow NFPA 70 Article 445 and NFPA 110 placement rules. Local amendments and the authority having jurisdiction govern.
Operation
Running cost combines fuel, oil and filter consumption, exercise runs, and load-factor effects such as wet stacking at chronic light load. Duty hours cap annual energy per the selected rating.
Maintenance
Oil, filter, coolant, battery, and overhaul schedules derive from engine hours and calendar limits, whichever arrives first, with warranty coverage checked against both.
Sources and baselines
Dated numbers, named sources, annual review.
Fuel and load baselines
Typical fuel consumption, oil quantities, and service intervals are labeled starting points with their source and data year. Manufacturer fuel tables and nameplate data replace them during verification.
Code references
Where practice is discussed, ISO 8528 ratings, NFPA 70 Article 445, and NFPA 110 are cited as context for why a rule exists, never as installation instruction. The locally adopted code and the authority having jurisdiction always govern.
Equipment figures
Typical wattages, COP ranges, and lifespans are labeled as starting points. Nameplate data and manufacturer sheets replace them during verification.
Verification protocol
Replace these five before relying on any result.
Manufacturer fuel table
Fuel consumption at 25/50/75/100% load for the exact model and fuel, with the data year stated.
Nameplate facts
Actual kW/kVA ratings, voltage, fuel type, and duty rating of the installed or quoted set.
Site conditions
Altitude, ambient temperature, ventilation, exhaust routing, and fuel storage that no generic model can see.
Qualified review
A licensed electrician, generator installer, or inspector confirms the conclusion before money is spent.
Fuel baselines are dated starting points, not live price feeds. Calculator results are screening outputs, not installer quotes, permits, or guarantees.
Known limits
What these tools deliberately do not do.
No code compliance
Nothing here determines whether an installation meets code. Sizing, protection, wiring methods, and clearances are field decisions under the AHJ.
No coincident-peak modeling
Load tools sum connected or average loads. Which loads coincide in the same 15-minute interval requires metered data the tools do not have.
No forecasts
Fuel-price and run-hour inputs project arithmetic, not the future. They show sensitivity to assumptions; they do not predict fuel prices, outages, or performance.
No site data
Public baselines never describe your site. Two identical loads at different altitudes or fuel prices can have legitimately different costs.