Every construction bid, schedule, and labor budget starts with a man-hour estimate. Get it wrong by 15% and you either lose the bid or lose money executing it. Man-hour estimating combines published unit rates (from databases like RS Means, Richardson, or company historical data) with site-specific productivity adjustments to predict how many labor hours a scope of work will require. The estimate then converts to crew sizes, durations, and calendar days to populate the project schedule.
The challenge is not finding unit rates—databases provide those. The challenge is accurately adjusting for the six productivity factors that can swing actual labor by 30–50% from the book rate: weather, site congestion, overtime fatigue, crew experience, supervision quality, and rework. This guide covers the estimating process, the adjustment factors, and the common mistakes that produce estimates disconnected from field reality.
Unit Rates and Crew Productivity
A unit rate expresses labor in hours per unit of installed work: man-hours per linear foot of pipe, per cubic yard of concrete, per each valve installed, per ton of steel erected. Published databases like RS Means provide these rates for hundreds of work items, calibrated to national average conditions with a crew of average skill and experience working a standard 40-hour week. The rates include not just the direct installation time but also material handling, layout, and incidental tasks that are part of a normal workday.
Crew productivity takes the unit rate one step further by defining the crew composition (e.g., 1 foreman + 2 journeymen + 1 apprentice + 1 laborer) and calculating output per crew-day. If a 4-person pipe crew can install 120 linear feet of 4-inch steel pipe per 8-hour day, and the project scope is 6,000 linear feet, the duration is 50 crew-days. The man-hours are 50 days × 4 people × 8 hours = 1,600 man-hours. This crew-based approach is more accurate than multiplying unit rates by total quantities alone because it accounts for crew interactions and the practical limit of how many people can work in a space simultaneously.
Company historical data is always more accurate than published databases because it reflects your specific crews, equipment, practices, and typical conditions. Maintain a feedback loop: track actual man-hours per unit on completed projects, compare to estimates, and build adjustment factors for future bids. Companies that do this consistently achieve estimate accuracy within ±5–8% on familiar work types, compared to ±15–25% when relying solely on published rates.
Job Labor Estimator
Estimate construction man-hours by trade and task with productivity adjustments for weather, overtime, site conditions, night shift, confined space, and elevated work.
The Six Productivity Factors
1. Weather (factor: 0.70–1.00): Extreme heat (>95 °F) reduces productivity by 15–30% due to mandatory rest breaks, PPE burden, and cognitive impairment. Cold weather (<32 °F) adds layered clothing that reduces dexterity, material handling difficulties (frozen ground, ice), and warm-up time. Rain and wind cause direct work stoppages. Budget weather days based on historical climate data for the project location and season—30-year averages from NOAA are a good starting point.
2. Site congestion (factor: 0.70–0.95): Congested sites (turnarounds, plant interiors, urban buildings) reduce productivity through restricted access, material staging constraints, interference between trades, and longer walking distances from laydown to work face. The more trades working in the same area simultaneously, the worse the congestion factor. A greenfield site with good access might warrant 0.95. A packed refinery turnaround with 40 crafts on top of each other might justify 0.70–0.75.
3. Overtime fatigue (factor: 0.85–0.95): Sustained overtime degrades productivity per hour worked. After 4 weeks of 50-hour weeks, productivity per hour drops to about 85% of baseline. At 60-hour weeks for 8+ weeks, it drops to 65–70%. The lost productivity on overtime hours often exceeds the extra output gained. 4. Crew experience (factor: 0.80–1.10): A highly experienced crew on familiar work can exceed book rates (1.05–1.10). A crew performing unfamiliar tasks or with many green hands may produce only 80–90% of book output. 5. Supervision ratio: Inadequate supervision (foreman-to-worker ratios exceeding 1:12 for complex work) directly reduces productivity through rework, idle time, and poor coordination. 6. Rework factor (1.02–1.15): Every project has some rework. Allow 2–5% for well-managed projects and 10–15% for fast-track or design-incomplete work.
Converting Man-Hours to Calendar Days
The conversion from man-hours to calendar days requires three inputs: total adjusted man-hours, crew size, and the work schedule. If the adjusted estimate is 3,200 man-hours, the crew is 8 people, and the schedule is 10 hours/day, 6 days/week: crew-hours per day = 8 × 10 = 80. Working days = 3,200 ÷ 80 = 40 working days. Calendar days (at 6 days/week) = 40 × 7/6 = 46.7, rounded to 47 calendar days. Add weather days, holidays, and mobilization/demobilization time to get the total duration.
The critical mistake is confusing man-hours with crew-hours. A 3,200 man-hour estimate does not mean 3,200 hours of elapsed time—it means 3,200 person-hours of effort. An 8-person crew working 10-hour days consumes 80 man-hours per calendar day. Dividing total man-hours by crew-hours-per-day gives working days, not calendar days. Always account for non-work days (weekends, holidays, planned shutdowns, weather days) when converting to calendar duration.
Also verify that the crew size is feasible for the work area. Putting 20 people in a 500-square-foot mechanical room does not halve the duration compared to 10 people—congestion losses may actually increase total man-hours. There is an optimal crew size for every work scope, beyond which adding people increases cost without reducing duration. Experienced estimators and superintendents know these limits intuitively; newer estimators should discuss crew sizing with field supervision before finalizing schedule durations.
Rain Day & Weather Delay Tracker
Track weather delay days against contract allowance, project schedule impact, and compare delay costs versus Saturday make-up work with regional precipitation benchmarks.
Common Estimating Mistakes
Optimism bias: Estimators consistently underestimate labor by 10–20% because they envision ideal conditions: full crews, no weather delays, no rework, no material wait time. Counter this by using historical actuals as a reality check and by applying productivity factors before finalizing the estimate, not as an afterthought.
Missing scope: The biggest man-hour busts come not from wrong unit rates but from incomplete quantity takeoffs. Missed items—hangers, supports, small-bore connections, temporary facilities, testing, and punch list work—individually seem minor but collectively add 10–20% to actual labor. Walk the drawings specifically looking for items that generate labor but are easy to overlook. On renovation and demolition work, the hidden conditions factor (asbestos, unforeseen structural conflicts, as-built inaccuracies) can add 15–30% to the estimate.
Ignoring learning curve: The first unit of any repetitive task takes significantly longer than the 50th. The construction learning curve (typically an 80–90% curve, meaning each doubling of cumulative quantity reduces per-unit time by 10–20%) should be factored into estimates for highly repetitive work like curtain wall installation, modular piping, or repetitive floor layouts. Conversely, one-off or unique installations should be estimated at the "first unit" rate, not the average from a database that assumes repetition.
Contingency and Escalation
Labor contingency accounts for the known unknowns: productivity losses you cannot predict specifically but know will occur. The appropriate contingency percentage depends on project definition: a detailed estimate from 100% complete drawings might carry 5–8% labor contingency. A conceptual estimate from 30% design might carry 15–25%. Standard industry guidelines (AACE International) define contingency ranges by estimate class, from Class 5 (conceptual, ±30–50%) to Class 1 (definitive, ±3–10%).
Labor rate escalation is separate from contingency and accounts for wage increases over the project duration. Union contracts typically specify annual increases of 2–4%. Open-shop rates follow market conditions. For multi-year projects, apply escalation to the labor cost in each future year at the expected rate. A 3-year project with $10 million in labor and 3% annual escalation costs $10.6 million when properly escalated—a $600,000 difference that can turn a profitable project into a loss if omitted from the bid.
On prevailing wage projects, escalation is especially important because Davis-Bacon wage determinations are updated annually and can increase by $2–5/hr per trade per year in active construction markets. The wage determination locked into your contract at bid may be superseded for option years or contract modifications. Build a prevailing wage escalation assumption into multi-year federal project bids, even if the current WD governs the base period.
Job Labor Estimator
Estimate construction man-hours by trade and task with productivity adjustments for weather, overtime, site conditions, night shift, confined space, and elevated work.