Estimation Methodology

ROM estimation principles and professional standards

Rough Order of Magnitude (ROM) Estimation

Definition and Purpose

ROM estimates are preliminary cost assessments used in the early phases of project planning. They provide order-of-magnitude pricing for budgeting, feasibility analysis, and conceptual design decisions.

Accuracy Expectations

ROM estimates typically have accuracy ranges of:

  • -25% to +75% for conceptual phase estimates
  • -15% to +30% for schematic design estimates
  • -10% to +20% for design development estimates

Appropriate Applications

  • Preliminary project budgeting
  • Feasibility studies and cost-benefit analysis
  • Design alternative comparisons
  • Value engineering exercises
  • Construction planning and scheduling

Calculator-Specific Methodologies

Concrete Calculator

Volume Calculations

Formula: Volume (cy) = Length × Width × (Thickness ÷ 12) ÷ 27

  • Assumes rectangular slab geometry
  • Includes 20% waste factor for typical pours
  • Does not account for complex forms or reinforcement

Cost Assumptions

  • Ready-mix concrete: $150/cy (regional average)
  • Labor: $75/hour × 0.5 hours/cy placement rate
  • Overhead & Profit: 10% each on materials and labor

Drywall Calculator

Area Calculations

Formula: Net Area = Total Area - Door Openings - Window Openings

  • Standard sheet sizes: 4'×8', 4'×12', 4'×16'
  • Waste factors: 10-20% based on complexity
  • Joint compound: ~0.8 lbs per sheet installed

Cost Assumptions

  • Drywall sheets: $15 each (1/2" standard)
  • Joint compound: $25 per 50-lb bucket
  • Labor: $45/hour × 0.02 hours/sqft installation rate

Paint Calculator

Coverage Calculations

Formula: Gallons = (Net Area × Coats) ÷ Coverage Rate

  • Coverage rates: 300-400 sqft/gallon based on surface
  • Rounds up to nearest quart for purchase quantities
  • Does not include primer (calculated separately)

Cost Assumptions

  • Quality paint: $45/gallon average
  • Labor: $50/hour × 0.015 hours/sqft application rate
  • Includes 10% material waste allowance

Insulation Calculator

R-Value Calculations

Formula: Thickness = Target R-Value ÷ R-Value per Inch

  • R-values per inch by material type
  • Limited by cavity depth constraints
  • Coverage based on standard bag/roll quantities

Cost Assumptions

  • Material costs: $1.20-$3.50/sqft by type
  • Labor: $55/hour × 0.025 hours/sqft installation rate
  • Includes climate zone considerations

Cost Structure and Markups

Base Material Costs

Material pricing reflects national averages and may vary significantly by region, supplier, and market conditions.

Labor Calculations

  • Base Rate: Skilled trade wages plus benefits
  • Productivity: Standard industry rates for normal conditions
  • Burden: 35% for payroll taxes, insurance, benefits

Overhead and Profit

  • General Overhead: 10% for office, equipment, administration
  • Profit: 10% margin on total project cost
  • Contingency: Not included - add separately based on risk

Limitations and Exclusions

General Limitations

  • Does not include site preparation or demolition
  • Assumes normal working conditions and access
  • Does not account for permit fees or inspections
  • Excludes specialty tools or equipment rental
  • Does not include material delivery charges

Regional Adjustments Required

  • Local material pricing variations
  • Prevailing wage requirements
  • Climate-specific installation considerations
  • Local building code requirements
  • Market competition and availability

Project-Specific Factors

  • Site accessibility and logistics
  • Schedule constraints and overtime
  • Quality specifications beyond standard
  • Coordination with other trades
  • Safety requirements and insurance

Professional Validation Process

Recommended Verification Steps

  1. Quantity Verification: Detailed takeoff using plans
  2. Market Pricing: Current quotes from suppliers/subcontractors
  3. Condition Assessment: Site visit and condition evaluation
  4. Risk Analysis: Identification of project-specific risks
  5. Contingency Planning: Addition of appropriate reserves

Quality Control

  • Independent review by qualified estimator
  • Comparison with historical project data
  • Validation against multiple sources
  • Documentation of assumptions and exclusions

Industry Standards and References

Professional Organizations

  • Association for the Advancement of Cost Engineering (AACE)
  • American Society of Professional Estimators (ASPE)
  • Royal Institution of Chartered Surveyors (RICS)

Reference Standards

  • AACE Recommended Practice 18R-97: Cost Estimate Classification System
  • AACE Recommended Practice 10S-90: Cost Engineering Terminology
  • RS Means Construction Cost Data (annual publications)

Building Codes and Standards

  • International Building Code (IBC)
  • International Energy Conservation Code (IECC)
  • Local amendments and regulations

Updates and Maintenance

Data Currency

Calculator data and pricing are updated quarterly to reflect market changes and industry trends. Users should verify current market conditions for active projects.

Formula Validation

Calculation methodologies are reviewed annually and updated based on industry feedback and best practice evolution.

User Feedback

We welcome feedback from construction professionals to improve accuracy and relevance of our estimation tools.

Contact for Technical Questions

For questions about estimation methodology or calculator technical details: