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Construction glossary · Estimating concepts

ROM in construction: what a R.O.M. (rough order of magnitude) estimate is

A ROM estimate — written R.O.M. and short for rough order of magnitude — is an early conceptual cost estimate prepared before design exists, used to test whether a project is financially feasible. ROM in construction is built from historical unit rates such as dollars per square foot rather than a quantity takeoff. Commonly cited accuracy ranges run from about minus 25 percent to plus 75 percent, and AACE International class 5 guidance allows even wider spreads.

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Updated August 2026 · Reviewed by the Ruh construction team

ROM = rough order of magnitudeAccuracy ~ -25% to +75%Used at concept stage

ROM estimate accuracy band

On the low side -25%On the high side +75%Rough order of magnitude, early-stage
The definition

ROM estimate, explained.

A ROM estimate is the first cost number a project team sees, usually prepared when the owner has little more than a site, a building size, and a use type. The punctuated form R.O.M. and the spelled-out rough order of magnitude mean the same thing, and ROM in construction almost always refers to this conceptual stage rather than any later pricing exercise: a ROM for construction work comes off a program sheet, not a drawing set. You will produce them during feasibility studies, developer pro formas, capital planning, and early design-build pursuits, often from a one-page program rather than drawings. Precon managers and chief estimators typically own them, because judgment matters more than math at this stage. The term shows up in budget letters and conceptual estimate deliverables; it does not belong on bid forms or pay applications. The most common mistake new estimators make is presenting a ROM as a single hard number. Always attach the accuracy range, the pricing date, escalation assumptions, and a written list of inclusions and exclusions, because the owner will remember the number long after they forget the caveats. The second mistake is anchoring low to please the room; a ROM that has to grow 40 percent at schematic design damages your credibility more than an honest wide range ever will.

How it is measured

ROM estimates are built from broad unit rates, most often dollars per square foot of gross floor area, sometimes dollars per unit (per bed, per hotel key, per parking stall) or per linear foot for utilities and roadway. The source is historical cost data: the contractor's own completed projects, adjusted for location, building size, scope differences, and escalation to the expected midpoint of construction, supplemented by published cost data where history is thin. There is no quantity takeoff at this stage beyond gross areas pulled from a program or massing sketch. The deliverable is usually a one-page or two-page budget letter labeled conceptual or AACE class 5, stating the basis of estimate, the accuracy range, and exclusions such as land, soft costs, and FF&E.

What is a ROM price?

A ROM price is the priced output of a ROM estimate: the dollar figure you get once the only quantity you have, usually gross floor area, is multiplied by a historical unit rate. The ROM estimate is the exercise; the ROM price is the number that goes in the budget letter. A ROM for construction is priced this way at every stage where drawings do not yet exist.

The worked example directly below produces one. A 40,000 sf tilt-up warehouse shell at $105 per sf carries through site work and a design contingency to a ROM price of $5.3 million. Because that figure comes from a unit rate rather than a takeoff, it is never presented alone: stated with the minus 25 percent to plus 75 percent range, the same ROM price reads as roughly $4.0 million to $9.3 million.

A ROM price is a planning number, not a bid, a quote, or a commitment. It carries a pricing date, escalation assumptions, and a written list of inclusions and exclusions, and it belongs in budget letters and conceptual estimate deliverables rather than on a bid form or a pay application.

Worked example

A worked ROM estimate example.

Worked example

An owner asks for a ROM on a 40,000 sf tilt-up warehouse shell. Your last three comparable tilt-up jobs averaged $105 per sf for the building shell, illustrative 2025 pricing. Building: 40,000 sf x $105/sf = $4,200,000. Site work on similar flat suburban sites has run about 15 percent of building cost: $4,200,000 x 0.15 = $630,000. Subtotal: $4,830,000. Add a 10 percent design contingency for the scope you cannot see yet: $4,830,000 x 0.10 = $483,000, bringing the ROM to $5,313,000, which you round and present as $5.3 million. Stated with a minus 25 percent to plus 75 percent range, that is roughly $4.0 million to $9.3 million ($5,313,000 x 0.75 = $3,984,750 and $5,313,000 x 1.75 = $9,297,750). The range looks wide because it is supposed to be; the single number is for planning, the range is the honest answer.

ROM rates and ROM fees

A ROM is expressed as a unit rate, not a lump sum you look up. The rate is what carries the pricing: above it is the $105 per square foot averaged from the last three comparable tilt-up jobs, applied to gross floor area. ROM rates come from the contractor's own completed projects, adjusted for location, building size, scope differences, and escalation to the expected midpoint of construction, supplemented by published cost data where that history is thin. Other jobs are rated per unit, per bed, per hotel key, per parking stall, or per linear foot for utilities and roadway, but the principle is the same: one broad rate against one gross quantity.

ROM fees is sometimes used loosely for that same unit rate, and the distinction is worth holding: a ROM is an estimate, not a quoted fee. Nothing in it is a price the contractor has offered to hold. The site work percentage and the design contingency in the example are judgment allowances on top of the rate, not line items anyone has priced, which is exactly why the accuracy range travels with the number.

How Ruh handles it

How Ruh handles ROM estimate.

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ROM estimate: frequently asked questions

How is a ROM estimate different from a detailed estimate?+

A ROM is priced from gross unit rates like dollars per square foot with no quantity takeoff, while a detailed estimate is built from measured quantities priced line by line against unit costs, sub quotes, and vendor pricing. A detailed estimate requires substantially complete drawings; a ROM needs only a program and a building type. Accuracy tightens accordingly, from a spread that can approach half the project value down to ranges commonly cited near plus or minus 5 to 10 percent for a definitive estimate.

Why is the ROM accuracy range wider on the high side than the low side?+

Because early unknowns mostly add cost rather than remove it. Scope tends to grow as design develops, site conditions and code requirements surface new work, and owners rarely shrink a program. Ranges like minus 25 percent to plus 75 percent reflect that asymmetry: a project is far more likely to land well above an early conceptual number than well below it.

Can a contractor commit to a price based on a ROM estimate?+

No. A ROM is a planning tool, not a bid, and committing to one as a fixed price is how contractors buy projects they regret. If an owner pushes for a commitment at the ROM stage, protect yourself with a written basis of estimate, a validity date, clearly stated exclusions, and contract language that converts the number to a GMP or lump sum only after a detailed, takeoff-based estimate on developed drawings.

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Related terms

Unit costContingencyAssembly estimatingHard costs

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Figures on this page are illustrative. Construction estimates depend on project-specific conditions, source documents, market pricing, and professional judgment. Ruh's AI assists the estimator and does not replace professional review: your team reviews, validates, and approves every estimate, bid, and pricing decision.

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