What sets your irrigation pumping cost per acre-inch
Pumping cost per acre-inch comes down to how much energy it takes to lift and pressurize each acre-inch of water, and what you pay for that energy. The lift and pressure part is measured as total dynamic head (TDH), in feet. The energy part depends on how efficiently your pump converts fuel or electricity into water horsepower, and on the price of whichever energy source runs the pump.
The Nebraska Pumping Plant Performance Criteria (NPPPC) gives a common yardstick for comparing energy sources: how many water horsepower-hours a well-maintained pumping plant should produce from one gallon of diesel, one gallon of propane, one MCF of natural gas, one gallon of gasoline, or one kWh of electricity. This calculator uses those criteria, adjusted for your own pump efficiency, to turn TDH into an actual cost.
| Energy source | Whp-hr per unit | Unit |
|---|---|---|
| Diesel | 12.5 | gallon |
| Gasoline | 8.66 | gallon |
| Propane (LP gas) | 6.89 | gallon |
| Natural gas | 61.7 | MCF (925 BTU/cf gas) |
| Electricity | 0.885 | kWh |
These figures assume a 75% pump efficiency, with a 5% drive loss for engine-driven units or an 88% electric motor efficiency, for a well-designed and well-maintained pumping plant. A pump running below that reference uses more fuel or electricity to pump the same water; this calculator scales the criteria by the ratio of 75% to the efficiency you enter to reflect that.
Prices vary by contract and location. Use your own recent fuel invoice or electric utility rate. A published state or regional average can be off by 20% or more from what you actually pay.
How this irrigation energy cost calculator works
The calculator converts total dynamic head into the water horsepower-hours needed per acre-inch, adjusts that figure for your pump's efficiency, converts it into fuel or electricity using the Nebraska criteria, and finally multiplies by your price.
1. Total dynamic head
TDH from lift and pressure
TDH (ft) = Static lift (ft) + 2.31 × Discharge pressure (psi)
2.31 feet of water column equals 1 psi. Add pipeline friction loss, in feet, to the lift if it isn't already included.
2. Water horsepower-hours per acre-inch
Whp-hr required
Whp-hr per acre-inch = TDH (ft) ÷ 8.75
Source: University of Nebraska–Lincoln Extension, CropWatch, "Comparing Fuel Sources for Irrigation." The constant 8.75 comes from the volume of an acre-inch (about 27,154 gallons) and the definition of water horsepower; it does not depend on pump efficiency.
3. Adjust for your pump's efficiency
Efficiency adjustment
Adjustment factor = 75 ÷ Your pump efficiency (%)
75% is the pump efficiency the Nebraska criteria assume for a well-maintained plant. A pump at 60% efficiency needs a factor of 75 ÷ 60 = 1.25, or 25% more energy than the reference.
4. Fuel or electricity required
Energy required per acre-inch
Fuel per acre-inch = (Whp-hr per acre-inch × Adjustment factor) ÷ NPPPC value for your energy source
5. Dollar cost
Cost
Cost per acre-inch = Fuel per acre-inch × Price per unit
Cost per season = Cost per acre-inch × Acres × Inches applied
When this calculator isn't the right tool
It estimates energy and dollar cost from TDH and pump efficiency. Use a different tool for:
- Water you buy by the acre-foot or by the meter, with no pump of your own, rather than energy you generate. See the irrigation water cost calculator.
- Checking whether your pumping plant is actually performing at the Nebraska reference, from a fuel-use test rather than an assumed efficiency. That comparison uses measured fuel or electricity records against the same NPPPC table, not this calculator.
- Sizing pipe or estimating friction loss itself. Add that to your TDH first using the PVC friction loss chart.
- Total system flow or well capacity rather than cost. See the irrigation well capacity calculator or the GPM per acre calculator.
Pumping cost calculation examples
A center-pivot system has a total dynamic head of 175 ft (static lift plus discharge pressure). The pump tests at 70% efficiency, and diesel costs $3.00 per gallon. The pivot covers 130 acres and applies 12 inches of water over the season.
- Whp-hr per acre-inch: 175 ÷ 8.75 = 20.0 whp-hr/ac-in.
- Adjustment factor: 75 ÷ 70 = 1.071.
- Diesel per acre-inch: (20.0 × 1.071) ÷ 12.5 = about 1.71 gallons per acre-inch.
- Cost per acre-inch: 1.71 × $3.00 = $5.14.
- Cost per season: 130 acres × 12 in = 1,560 acre-inches. 1,560 × $5.14 = about $8,023.
An electric well pump
A well pump has a total dynamic head of 105 ft, tests at 65% efficiency, and runs on electricity at $0.11 per kWh, irrigating 50 acres with 8 inches applied for the season.
- Whp-hr per acre-inch: 105 ÷ 8.75 = 12.0 whp-hr/ac-in.
- Adjustment factor: 75 ÷ 65 = 1.154.
- Electricity per acre-inch: (12.0 × 1.154) ÷ 0.885 = about 15.65 kWh per acre-inch.
- Cost per acre-inch: 15.65 × $0.11 = $1.72.
- Cost per season: 50 acres × 8 in = 400 acre-inches. 400 × $1.72 = about $688.
Comparing the two examples shows why TDH, not fuel choice alone, usually drives the biggest differences: the diesel pivot's higher head accounts for most of its higher per-acre-inch cost, separate from which energy source is used.
Measuring your inputs
Finding total dynamic head
Static lift is the vertical distance from the water surface under pumping conditions (not the resting water level) to the pump discharge. For a well, this means the pumping water level after drawdown, not the static water level before the pump starts. Discharge pressure is read directly from a pressure gauge at the pump outlet while the system is running at normal load. Convert psi to feet by multiplying by 2.31, then add any pipeline friction loss between the pump and the field.
Getting a real pump efficiency number
Nameplate or catalog efficiency describes a new pump under lab conditions, not the one currently installed. A field pumping plant test, measuring flow rate, TDH and fuel or electricity use over a timed period, gives an actual efficiency figure. If you don't have a recent test, a rule of thumb is to assume efficiency has dropped from a new pump's rating with age and hours of use, and to treat any number you enter here as an estimate to refine once you have test data.
Common mistakes
- Using the resting water level instead of the pumping (drawdown) level for static lift, which understates TDH and cost.
- Leaving out pipeline friction loss on long or undersized mainlines.
- Mixing up natural gas units. Utility bills are often in therms or hundred cubic feet (CCF), not MCF; convert before entering a price here.
- Entering a catalog pump efficiency instead of a tested one, especially on an older pump.
Factors that change your pumping cost
The calculator only knows what you enter. These are the main reasons the real number moves.
| Factor | Effect on cost | What to adjust |
|---|---|---|
| Well drawdown | A well that draws down more under pumping raises static lift as the season goes on. | Use a pumping water level measured during use, not before startup. |
| System operating pressure | Higher-pressure sprinkler packages add directly to TDH. | Enter the actual discharge pressure at normal operation. |
| Pipeline friction loss | Long or undersized mainlines add head that isn't obvious from lift alone. | Add friction loss, in feet, to the lift before entering TDH. |
| Pump condition | Worn impellers, damaged seals, or a pump mismatched to current pressure all lower efficiency. | Use a tested efficiency, not a catalog rating. |
| Energy price | Sets the dollar cost directly once fuel or electricity per acre-inch is known. | Use your most recent invoice or rate, not a regional average. |
| Acre-inches applied | More irrigations or a longer season multiply the per-acre-inch cost. | Total the depth from all irrigations for the seasonal figure. |
Of these, pump condition is the one producers most often underestimate. A plant testing at 50% of the Nebraska reference is not unusual on an aging system, and it roughly doubles the fuel needed for the same water. A periodic pumping plant test is the only way to know where your own pump stands.
Frequently asked questions
What is a water horsepower-hour and why does it matter for pumping cost?
A water horsepower-hour (whp-hr) is the actual work done on the water itself: lifting it and pushing it through the discharge pressure, for one hour at one horsepower. It depends only on total dynamic head and the volume pumped, not on your pump or engine. Irrigation Calculators uses it as the common yardstick to compare diesel, propane, natural gas, gasoline and electric pumping plants on equal terms, following the Nebraska Pumping Plant Performance Criteria.
How does this calculator use the Nebraska Pumping Plant Performance Criteria?
The Nebraska Pumping Plant Performance Criteria (NPPPC) states how many water horsepower-hours a well-maintained pumping plant should produce from one unit of energy: about 12.5 per gallon of diesel, 8.66 per gallon of gasoline, 6.89 per gallon of propane, 61.7 per MCF of natural gas, or 0.885 per kWh of electricity. This calculator divides the water horsepower-hours your pump must produce by that figure, adjusted for your own pump efficiency, to estimate how much fuel or electricity you actually need.
How do I find my pump's total dynamic head?
Total dynamic head (TDH) is the static lift from the water source to the pump discharge, plus the pressure at the discharge outlet converted to feet (multiply psi by 2.31), plus any friction loss in the pipeline. If you already have a TDH figure from a pump curve or system design, enter it directly. Otherwise use the lift-plus-pressure option and add pipeline friction loss from a chart such as the PVC friction loss chart if the line is long or narrow.
How much does pump efficiency change my pumping cost?
A lot. The Nebraska criteria assume a 75% pump efficiency for a well-maintained plant. If your pump only tests at 60%, you need 75 divided by 60, or about 25% more fuel or electricity, to move the same water the same distance. Worn impellers, damaged seals, and a pump mismatched to its current pressure are the most common reasons efficiency drops below that reference.
Which is cheaper to pump with: diesel, electricity, propane or natural gas?
It depends entirely on your local prices, not just the Nebraska whp-hr figures. Run each energy source through this calculator with your own price to compare them directly in dollars per acre-inch. A fuel with a lower whp-hr rating, like propane, can still be the cheaper option if it costs enough less per unit than the alternatives in your area.
What is an acre-inch of water?
An acre-inch is the volume of water that covers one acre to a depth of one inch: 3,630 cubic feet, or about 27,154 gallons. It's the standard unit for pricing and reporting irrigation water in the United States, which is why pumping costs are usually expressed per acre-inch rather than per gallon.
See the acre-inches calculator to convert from acre-feet or total gallons.
How can I lower my irrigation energy cost per acre-inch?
Reduce total dynamic head where you can, such as by lowering system operating pressure or fixing a high-friction pipeline. Keep the pump efficiency close to the 75% reference with regular maintenance and a periodic pump test. Beyond the pumping plant itself, applying only the water the crop needs, tracked with an evapotranspiration-based schedule, cuts the number of acre-inches you pump in the first place.
Does this calculator include pipeline friction loss?
Only if you include it in the total dynamic head you enter. If you use the lift-plus-pressure option, add your pipeline's friction loss, in feet, to the lift figure before you enter it, since this calculator does not calculate friction loss itself. The PVC friction loss chart gives typical loss rates by pipe size and flow.
See the PVC friction loss chart.
Why does this calculator only use US units?
The acre-inch has no standard metric equivalent, and the Nebraska Pumping Plant Performance Criteria is published entirely in US customary units: feet of head, psi, gallons, MCF and kWh. Converting the criteria itself to metric would risk introducing rounding errors not present in the source, so this calculator keeps the source's own units throughout.
Who built and checked this calculator
Licensed Professional Engineer and Irrigation Association Certified Irrigation Designer with more than 20 years in irrigation design, system auditing and landscape water management. Full profile
How this page was checked
- Formula and both worked examples verified by hand against the calculator's code.
- Nebraska Pumping Plant Performance Criteria values cross-checked against three independent extension sources.
- Methods follow University of Nebraska–Lincoln and USDA NRCS pumping plant evaluation practice.
Sources
- van Donk, Simon, University of Nebraska–Lincoln Extension, CropWatch. Comparing Fuel Sources for Irrigation.
- Dorn, Thomas W., University of Nebraska–Lincoln Extension. Using Your Records to Locate Inefficient Pumping Plants.
- Rogers, Danny H., Kansas State University Research and Extension. Comparing Irrigation Energy Costs (MF2360).
- USDA Natural Resources Conservation Service. Complete Pumping Plant Evaluation for Energy Savings (E533B).
- Melvin, Steven, University of Nebraska–Lincoln Extension. Reducing the Cost of Pumping Irrigation Water.