What is a Lang factor?
A Lang factor is a multiplier used to estimate total process plant cost from the combined cost of major equipment. For example, a factor of 3.63 means an estimated plant cost of 3.63 times the equipment total, including the equipment itself.
The original factors use delivered equipment cost. Match the cost basis and included project scope to whichever factor you select.
Estimate basis
Major equipment costs
Add the major equipment items included in your estimate basis.
Have a quote for a different equipment size? Use the equipment cost scaling calculator first, then reconcile its cost date, currency, and purchased or delivered cost basis before entering the result here. A scaling exponent changes equipment cost with size; a Lang factor estimates plant cost from equipment cost.
Results
Equipment subtotal
| Equipment | Qty | Unit cost | Subtotal |
|---|
Compare factors for this plant type
Each row applies a different multiplier to the same equipment total. This is a sensitivity comparison, not a confidence interval or an adjustment for differences in scope.
| Source | Factor | Factored estimate |
|---|
Worked example: equipment cost to plant cost
Select Original Lang, Mixed solid-fluid processing, and USD. The Load example button fills the equipment list below. For this illustration, assume every price is a delivered equipment cost at the same cost date and location.
| Equipment | Quantity | Unit cost | Subtotal |
|---|---|---|---|
| Reactor | 1 | $600,000 | $600,000 |
| Heat exchanger | 2 | $180,000 | $360,000 |
| Pump package | 3 | $75,000 | $225,000 |
| Storage vessel | 2 | $140,000 | $280,000 |
| Delivered equipment total | $1,465,000 | ||
The estimated non-equipment portion is $5,317,950 − $1,465,000 = $3,852,950. Do not add the equipment cost a second time. Review excluded scope separately; this is a screening estimate, not a quotation or a guaranteed accuracy range.
How to use the Lang factor method
- List the major equipment and multiply each unit cost by its quantity.
- Put every cost on the same currency, date, location and equipment basis. Original Lang uses delivered equipment cost.
- Choose the plant type and a factor appropriate to the project scope.
- Multiply the equipment total by that factor, then review exclusions separately.
Use one overall factor, not the sum or product of several factor sets. The factor already includes the equipment itself. The non-equipment portion is (factor − 1) × equipment cost.
Plant type: Choose solid for predominantly solids processing, mixed for substantial solids handling together with liquids or gases, and fluid for predominantly liquid or gas processes. Dysert and Wolf are offered only for fluid comparisons; missing values are not zero.
Typical Lang factors by plant type
Start with a factor calibrated to comparable completed projects, if you have one. Otherwise use a published set as an early screening assumption and compare alternatives. A larger factor produces a higher estimate; it is not automatically more accurate, more current, or an adequate contingency allowance.
| Factor source | Solid | Mixed | Fluid |
|---|---|---|---|
| Original Lang | 3.10 | 3.63 | 4.74 |
| AACE RP 59R-10, as reported | 3.89 | 5.04 | 6.21 |
| Perry’s handbook, as reported | 3.80 | 4.10 | 4.80 |
| Dysert worked example | Not provided | Not provided | 5.10 |
| Wolf database benchmark | Not provided | Not provided | 5.12 |
The supplied comparison is Table 2 in Wain (2014). Its AACE and Perry attributions are retained as reported values: the complete source tables were not independently verified here. The AACE public preview does not expose the factor table. Wain cites Perry’s 7th edition (1997), p. 9-68. These presets are not represented as current AACE recommendations.
Original Lang
Use when: establishing a familiar historical baseline for a conventional process plant.
Strength: simple, transparent, and differentiated by process type. AACE’s cost-engineering text confirms the three values and describes a plant scope including process units and offsites.
Check: the original method uses delivered equipment cost. Verify freight and scope before applying it to vendor purchase prices. Modern site conditions can differ substantially.
AACE RP 59R-10, reported set
Use when: comparing your screening result with the higher factor set attributed to the 2011 RP in the supplied table.
Strength: offers a separate benchmark for all three plant types.
Check: consult the full RP for equipment basis and scope before using this as your adopted estimate. Do not interpret 6.21 as a universally recommended fluid-plant factor or a 2026 cost update.
Perry’s handbook, reported set
Use when: comparing an early estimate with the handbook values quoted in the supplied table.
Strength: provides another three-category reference for sensitivity checks.
Check: confirm the cited edition’s basis and inclusions. These values are historical; the calculator does not establish that they apply to a particular technology, geography, or project scale.
Dysert worked example
Use when: checking a fluid-process estimate against an example with explicit direct costs, field indirects, home-office costs, commissioning, and contingency.
Strength: makes the build-up behind the overall ratio understandable.
Check: 5.10 is a rounded ratio from a worked example, not an independently fitted factor for every fluid plant. The example includes contingency; adding another allowance without reconciling scope can double count it.
Wolf database benchmark
Use when: benchmarking a roughly comparable refinery or petrochemical project.
Strength: Wolf reports an average near 5.12 from a database dominated by these industries, providing an empirical cross-check.
Check: the underlying ratios vary widely. The average is neither a guarantee nor a solids-plant factor. Confirm the contractor installed-cost scope and separately identify any excluded owner costs.
Custom project/company factor
Use when: you have reliable completed-project data with similar technology, location, scale, and execution approach.
Strength: can reflect your actual cost structure. Calculate the ratio of comparable installed plant cost to equipment cost after normalizing the data.
Check: define the numerator and denominator consistently, investigate outliers, and avoid calibrating to a single atypical project. This calculator requires a factor of at least 1 because its total includes the entered equipment cost.
Lang factor limitations and cost basis
- Use the same currency, cost date, and location basis throughout. This tool does not perform escalation or currency conversion.
- Do not multiply an already installed package price by a whole-plant factor without adjusting for scope already included.
- Record what is included for piping, civil work, buildings, utilities, offsites, engineering, commissioning, taxes, and contingency. Add allowances only for demonstrably excluded scope.
- Identify land, working capital, owner costs, unusual site work, and major infrastructure separately. “Total plant cost” is not automatically the complete investment requirement.
- Use more detailed estimating for unusual equipment, extensive brownfield tie-ins, or major infrastructure. A generic factor cannot resolve these costs.
Equipment factoring supports early feasibility work. Selecting a named factor does not assign an AACE estimate class or guarantee an accuracy range; project definition and risk still matter.
Lang factor questions
Does the Lang factor include the equipment cost?
Yes. The factored total already includes the equipment. For a factor of 3.63, the estimated non-equipment portion is 2.63 times the equipment total.
Is the Lang factor the same as the six-tenths rule?
No. A Lang factor estimates plant cost from equipment cost. The six-tenths rule scales an equipment cost with capacity using an exponent of 0.6. Use the equipment cost scaling calculator to explore capacity changes before estimating plant cost.
How accurate is a Lang factor estimate?
There is no single accuracy range for every project. The equipment list, cost basis, scope and similarity to the reference projects determine whether the estimate is useful. Compare factor assumptions for early screening and develop a detailed estimate as the design matures.
Sources and verification
- Wain (2014), Updating the Lang Factor, Table 2 and references: provenance of the supplied comparison.
- AACE, Skills and Knowledge of Cost Engineering, 6th edition, Chapter 9: classic values, scope distinctions, and the example ratio of 5.1 including contingency.
- AACE RP 59R-10 public preview: confirms the recommended practice and its conceptual-estimating purpose; full factor table is outside this preview.
- Dysert, Sharpen Your Cost Estimating Skills, Cost Engineering 45(6), June 2003, pp. 25–26: worked example. Readable reproduction.
- Wolf, Lang Factor Cost Estimates (2013): database context and 5.12 average. Archived reproduction; original author website was unavailable during verification.
Equation values and input guide
Choose a factor set whose equipment and plant cost boundaries match your estimate. Enter quantity and unit equipment cost for each item in one currency and price date. Use a custom factor only with a documented comparable basis.
- Equipment subtotal
- Σ(quantity × unit equipment cost). Σ means sum over every included equipment item; quantity is a count and cost is per item.
- Lang factor
- Dimensionless multiplier converting the equipment subtotal to the defined overall plant-cost scope. It already includes the equipment within that scope; do not add it again.
- Estimated plant cost
- Equipment subtotal multiplied by the selected factor, in the entered currency. It remains an early estimate, not a quotation.
- Plant type and factor source
- Choices that determine the multiplier. Check each source’s included costs, equipment delivery basis, date and exclusions before using its number.
Use the unit selectors beside the inputs. Units shown in the equations must be consistent when checking the math by hand.