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Propane (LPG) Power & Fuel Engine

Propane Generator Sizing Calculator

Calculate your exact propane (LPG) generator kW requirements, fuel consumption rate (GPH, BTU/hr), backup runtime across 20lb to 1,000gal tanks, running costs, and cold weather vaporization limits.

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1 Electrical Load Input

Select appliances from category lists or search the master library to calculate total running and surge wattage.

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2 Propane Tank & System Setup

Fuel Source & Environment
$
Propane delivers ~10% less peak energy per cylinder cycle than gasoline.

Calculation Results

Recommended LP Generator Size
10.0 kW (12.5 kVA @ 0.8 PF)
Minimum Generator Spec: 8.4 kW 20% Buffer
Total Running Watts 5,000 W 41.7 Amps @ 120V
Total Surge Watts 8,500 W 35.4 Amps @ 240V

Propane Fuel Consumption Rate

Gal / Hour 0.60 gal
Lbs / Hour 2.54 lbs
BTU / Hour 54,900
Cu.Ft / Hr 21.8 cu ft
Selected Tank Runtime (100 lb Tank) 18.9 Usable Gal
31.5 Hours (~1.3 Days Continuous)
$65.15 Total Tank Refill Cost
Vaporization Rate Check Passed

Your 100 lb tank can comfortably vaporize 110,000 BTU/hr at 0°F, easily exceeding your generator's 54,900 BTU/hr demand without freezing up.

Outage Fuel Cost Projections @ $3.45/gal
1 Hour Continuous Run $2.07
24 Hours Continuous Run $49.68
3-Day Power Outage (72 hrs) $149.04
7-Day Major Grid Outage (168 hrs) $347.76

Propane Tank Runtime Comparison Matrix

Estimated continuous runtime for your current 5,000 W load across standard liquid propane tanks.

80% Safe Tank Liquid Fill
Propane Tank Size Total Capacity Usable Fuel (80%) Total BTUs Continuous Runtime Days of Backup Refill Cost

Comprehensive Propane Generator Sizing Reference Table

Standard LP generator sizes, fuel consumption rates at 25%, 50%, 75%, 100% load, and tank runtimes.

Generator Rating Running Watts Surge Watts Fuel @ 25% Load Fuel @ 50% Load Fuel @ 75% Load Fuel @ 100% Load Runtime on 20lb Tank Runtime on 100lb Tank Runtime on 250gal Tank
2.0 kW (2,000W) 1,600 W 2,000 W 0.12 GPH 0.18 GPH 0.24 GPH 0.31 GPH 21 Hours 105 Hours 1,111 Hours
3.5 kW (3,500W) 3,000 W 3,500 W 0.19 GPH 0.31 GPH 0.42 GPH 0.52 GPH 12 Hours 61 Hours 645 Hours
5.5 kW (5,500W) 4,800 W 5,500 W 0.32 GPH 0.50 GPH 0.68 GPH 0.85 GPH 7.5 Hours 38 Hours 400 Hours
7.5 kW (7,500W) 6,500 W 7,500 W 0.45 GPH 0.72 GPH 0.98 GPH 1.22 GPH 5.2 Hours 26 Hours 277 Hours
10.0 kW (10,000W) 8,500 W 10,000 W 0.58 GPH 0.95 GPH 1.32 GPH 1.65 GPH 4.0 Hours 20 Hours 210 Hours
12.0 kW (12,000W) 10,000 W 12,000 W 0.70 GPH 1.18 GPH 1.62 GPH 2.02 GPH 3.2 Hours 16 Hours 169 Hours
14.0 kW (Standby) 14,000 W 15,500 W 0.92 GPH 1.50 GPH 2.10 GPH 2.65 GPH 2.5 Hours 12.6 Hours 133 Hours
18.0 kW (Standby) 18,000 W 20,000 W 1.20 GPH 1.95 GPH 2.75 GPH 3.48 GPH 1.9 Hours 9.7 Hours 102 Hours
22.0 kW (Standby) 22,000 W 24,000 W 1.45 GPH 2.35 GPH 3.30 GPH 4.20 GPH 1.6 Hours 8.0 Hours 85 Hours
26.0 kW (Standby) 26,000 W 29,000 W 1.70 GPH 2.78 GPH 3.90 GPH 4.95 GPH 1.3. Hours 6.8 Hours 72 Hours

Propane Calculation Engineering Formulas & Energy Constants

Step-by-step mathematical expressions used by our 100% accurate calculation engine.

1. Fuel Consumption Rate Formula

Propane generator fuel consumption rate ($C_{GPH}$) in gallons per hour is derived from electrical power load ($P_{kW}$) and thermal heat engine efficiency ($HR_{BTU/kWh}$):

CGPH = (PkW × Load% × HeatRateBTU/kWh) / 91,500 BTU/gal

Where standard LP internal combustion engine heat rate = 11,000 BTU/kWh, and 1 Gallon of LP = 91,500 BTU.

2. Tank Backup Runtime Formula

Total continuous backup runtime ($T_{hours}$) is calculated using the usable liquid volume ($V_{usable}$) in gallons:

Usable Gallons = Total Tank Gallons × 0.80 (80% Safety Fill)
Runtime (Hours) = Usable Gallons / CGPH

For propane cylinders measured in lbs (e.g. 20lb, 100lb): 1 Gallon LP = 4.24 lbs.

3. Required Generator kW Sizing Formula

Total continuous generator size ($kW_{rec}$) incorporates running load, altitude derate, temperature derate, and safety margin:

kWrec = (Total Running Watts / 1000) × (1 + SafetyMargin%) / (DerateAlt × DerateTemp × DerateLPG)

DerateLPG = 0.90 if generator peak rating is calibrated on gasoline.

4. Propane Energy Conversion Constants

  • 1 Gallon Liquid Propane: 91,500 BTU = 4.24 lbs = 36.39 $FT^3$ Vapor
  • 1 Pound Liquid Propane: 21,556 BTU = 0.236 Gallons
  • 1 Cubic Foot LP Vapor: 2,516 BTU
  • Electrical Equivalent: 1 kWh = 3,412 BTU electrical (31% engine efficiency = ~11,000 BTU thermal fuel input per kWh)