Engineering Estimating Guides

Electrical

#1 Sizing THHN Conductors per PEC Table 3.10.1 — A Worked Example

Load current, the 125% continuous rule, correction factors, termination ratings, and a voltage-drop check — worked end to end.

#2 Voltage Drop Calculation for Branch Circuits and Feeders

The 3% and 5% rules, the single-phase and three-phase formulas, and how to find the conductor size that keeps you inside both.

#3 How to Build an Electrical Panel Schedule from a Load List

From a raw circuit list to a balanced panel schedule: phase balancing, connected vs demand load, spare ways, and main breaker sizing.

#4 Distribution Transformer Sizing for Buildings

kVA from demand load and power factor, standard sizes, load-growth allowance, and the impedance and vector-group details that matter for the BOQ.

#5 Standby Generator (Genset) Sizing for Commercial Buildings

Running kW is only half the job — motor starting kVA, step loading, and site derating decide the real generator size.

#6 Applying PEC Demand Factors to Lighting, Receptacle, and Appliance Loads

Why 30 kVA connected can legally be 14 kVA of demand — the PEC demand-factor tables, worked on a real house.

#7 Short-Circuit Current and Interrupting Capacity — Basics for Estimators

The infinite-bus method, transformer %Z, and why the wrong AIC rating turns a breaker into a bomb.

#8 Conduit and Raceway Fill Calculation per PEC

The 53 / 31 / 40 percent rule, conductor cross-sectional areas, and a worked EMT sizing example.

#9 Grounding and Bonding System Design per PEC Article 2.50

Grounding electrode vs equipment grounding vs bonding — three different jobs, three different sizing rules.

#10 Power Factor Correction — Sizing a Capacitor Bank

The kVAR formula from tan phi, step sizing, and why over-correction and harmonic resonance can cost more than the penalty you were fixing.

#11 Lighting Design by the Lumen Method — Fixtures and Circuits

Target lux, the lumen-method formula, room index, and how the fixture count becomes lighting circuits in the panel.

#12 Preparing an Electrical Riser / Single Line Diagram for Permit

What the SLD must show for a building permit — service entrance, protection, feeders, panels, and load summary on one sheet.

#13 Estimating an Electrical Bill of Materials from a Circuit Schedule

Turning a panel schedule into priced quantities — homerun logic, vertical drops, wastage, fittings ratios, and device counts.

#14 Motor Feeder and Branch Circuit Sizing per PEC

Use table FLC not nameplate, conductors at 125%, branch protection up to 250%, overloads at 115–125% — the four different multipliers explained.

EE Tools

#15 Wire Sizing by Ampacity vs Voltage Drop — Which Governs?

On short runs the ampacity table wins; past a crossover length, voltage drop takes over. Here is how to find that length.

#16 Reading PEC Table 3.10.2.6(B) — 60 °C Conductor Ampacities

Why small circuits are sized on the 60 °C column even when the wire is rated 90 °C — and how the temperature correction still uses the higher column.

#17 The 40% Conduit Fill Rule Explained (3 or More Conductors)

One wire 53%, two wires 31%, three or more 40% — the physical reason each number is what it is.

#18 Single-Phase vs Three-Phase Motor Circuits — FLA, Wire, and Breaker

Same horsepower, very different current: the root-3 factor, table FLC values, and how wire and breaker sizing diverge.

#19 Ampacity Correction Factors for Ambient Temperature and Bundling

Hot ceilings and crowded conduits both steal ampacity — and the two factors multiply.

#20 Sizing the Grounding Electrode Conductor and Ground Rods

GEC from the service size, the 14 mm² cap for rod connections, two rods 1.8 m apart, and the 25-ohm test.

Plumbing

#21 WSFU vs DFU — Supply and Drainage Fixture Units Compared

Two fixture-unit systems, two sets of tables, two different jobs — and why one water closet is 6 units on the supply side but 4 on the drain side.

#22 Drainage Stack and Building Drain Sizing by Fixture Units

Total the DFU per branch, stack, and building drain, read the table at the right slope, and respect the offset rules.

#23 Vent Pipe Sizing — Individual, Branch, and Stack Vents

Vents protect trap seals. Size them by the drain they serve, the developed length, and the one-third-diameter rule.

#24 Estimating Peak Water Demand for a Multi-Storey Building

From fixture units to litres per second with Hunter’s curve — then storage, pump, and riser sizing follow.

#25 Sizing a Domestic Water Booster Pump — Flow and Total Dynamic Head

Flow from peak demand, head from static lift plus friction plus residual pressure — then pick the pump off its curve.

#26 Hot Water System Sizing — Heater Capacity and Recirculation

Storage vs continuous-flow, the recovery-rate formula, and why a recirculation loop is a comfort and code decision.

#27 Septic Tank and Soak Pit Sizing for Residential Projects

Tank volume from population and retention time; soak pit area from a percolation test — the two-step method.

#28 Storm Drainage and Roof Drain Sizing by Rainfall Intensity

The rational method, local rainfall intensity, and why every roof needs a secondary (overflow) drainage path.

#29 Choosing Pipe Material — PPR, PEX, uPVC, and Cast Iron

Pressure vs gravity, temperature, jointing method, and cost — the four questions that pick the pipe.

#30 Plumbing Rough-In Takeoff — Fittings, Valves, and Hangers

Pipe length is the easy part. Fittings ratios, valve counts, hanger spacing, and sleeve counts are where takeoffs leak money.

Structural

#31 Rebar Quantity Takeoff and the Bar Bending Schedule

Cutting length = clear span + hooks + laps + bends deduction. Then multiply by unit weight and add wastage.

#32 Formwork Contact Area Takeoff for Slabs, Beams, and Columns

Formwork is measured as the area of concrete it touches — with specific rules for each element.

#33 Concrete Mix Ratios — 1:2:4, 1:1.5:3, and 1:1:2 by Strength

Nominal mixes map roughly to strength classes — and to very different cement quantities per cubic metre.

#34 Cement, Sand, and Gravel Quantities per Cubic Meter of Concrete

The 1.54 dry-volume factor, the ratio split, and a table you can estimate from directly.

#35 Concrete Hollow Block (CHB) Wall Takeoff — Blocks, Mortar, Rebar

12.5 blocks per square metre, mortar by bedding volume, vertical bars by spacing, and plaster both faces.

#36 Rebar Lap Splice and Development Length — 40d, Hooks, and Ties

Why 40 diameters, where laps are allowed, and how splice allowances add real tonnage to the estimate.

#37 Structural Steel Weight Takeoff from Member Schedules

Section mass per metre × length, plus connections, base plates, and a fabrication wastage allowance.

#38 Slab-on-Grade Estimation — Concrete, Mesh, Vapor Barrier

Volume from area × thickness plus a subgrade tolerance, mesh with laps, and the layers underneath the slab.

#39 Isolated and Combined Footing Takeoff

Excavation, lean concrete, structural concrete, two-way rebar mats, and backfill — computed per footing type from the schedule.

#40 Estimating Suspended Slab Formwork, Shoring, and Reshoring

Slab soffit area sets the formwork; concrete strength gain and construction cycle set how many sets of shoring you need on site.

Solar PV

#41 Peak Sun Hours — The One Number That Sizes Your Array

PSH is daily irradiation expressed as hours of full sun. It turns a kWh target into a kWp array size.

#42 Grid-Tied vs Hybrid vs Off-Grid — Choosing the System Type

Batteries, backup, and export rules decide the topology — and the topology decides half the BOM.

#43 Inverter Sizing and the DC:AC Ratio Explained

A 1.1–1.3 DC:AC ratio deliberately oversizes the array so the inverter runs near rated output more of the day.

#44 PV String Sizing — Panels in Series Within MPPT Voltage Limits

Cold mornings raise Voc and can trip the inverter; hot afternoons drop Vmp below the MPPT window. Size for both extremes.

#45 MPPT Input Sizing — Strings per Tracker and Current Limits

Each MPPT has a maximum input current and a short-circuit limit. Parallel only as many strings as it can track and protect.

#46 Battery Bank Sizing for Off-Grid and Hybrid Solar

Usable capacity = daily load × autonomy ÷ depth of discharge ÷ system efficiency. Chemistry sets the DoD.

#47 Solar DC and AC Cable Sizing per PEC and NEC 690.8

PV source circuits carry 1.56 × Isc for sizing; then voltage drop (1% DC target) usually pushes the cable one size larger.

#48 DC and AC Surge Protection for PV Systems

A rooftop array is a lightning target on a 25-year contract. Type 2 SPDs on both DC and AC sides are cheap insurance.

#49 Solar Mounting and Racking Takeoff for Metal and Concrete Roofs

Rails by panel rows, clamps by module count, roof attachments by wind zone spacing — plus flashing and ballast.

#50 Net Metering in the Philippines — Sizing to the Export Cap

Net metering is capped at 100 kW and credits exports at the blended generation rate, not the full retail rate — size for self-consumption.

#51 Solar Financial Analysis — Payback, ROI, and 25-Year Cashflow

Simple payback is the headline; the 25-year cashflow with degradation and tariff escalation is the real story.

#52 Building a Load Profile for Accurate Solar Sizing

Monthly kWh sizes the array; the hour-by-hour shape decides how much you self-consume and whether you need a battery.

#53 Panel Technology for Estimators — Mono PERC, TOPCon, Bifacial

Efficiency, temperature coefficient, degradation, and bifacial gain — the four spec-sheet numbers that change the BOM.

#54 The Complete Solar PV Bill of Materials Checklist

Modules and inverter are 55% of the cost. The other 45% is the list people forget — here it is in full.

Civil

#55 The Average End Area Method for Cut and Fill Volumes

Two cross-section areas, the distance between them, and a simple average — with the prismoidal correction for accuracy.

#56 Swell and Shrinkage Factors — Bank, Loose, and Compacted Soil

One volume of soil is three different numbers depending on whether it’s in the ground, in the truck, or in the fill.

#57 Trench Excavation, Bedding, and Backfill Takeoff by Pipe Size

Trench width from pipe OD plus working clearance, then subtract pipe and bedding from the dig to get backfill.

#58 Road Pavement Layer Takeoff — Subgrade to Wearing Course

Each layer is area × compacted thickness × bulking — plus prime coat, tack coat, and the widening for shoulders.

#59 Aggregate Base and Sub-Base Course Quantity Estimation

Compacted volume is the spec; delivered volume is compacted × a bulking factor; tonnes are volume × density.

#60 Reinforced Concrete Pipe Culvert and Headwall Takeoff

Pipe by the metre, bedding and headwalls in concrete and rebar, plus excavation, backfill, and scour protection.

#61 Site Clearing, Grubbing, and Topsoil Stripping Quantities

Clearing is by area, tree removal by count and girth, topsoil by area × depth — and stripped topsoil is an asset, not just spoil.

#62 Estimating Retaining Wall Concrete, Rebar, and Backfill

Stem and base concrete per metre of wall, two-face rebar mats, granular backfill with drainage, and the weep-hole and geotextile lines.

FDAS / Fire

#63 Smoke Detector Spacing per NFPA 72 — The 0.7 Spacing Rule

Start from 9.1 m listed spacing, apply the 0.7 factor for the worst corner, then adjust for beams, ceilings, and airflow.

#64 Heat Detector Spacing and Listed Spacing Adjustment

Heat detectors have shorter listed spacing than smoke, and it shrinks further as the ceiling gets higher.

#65 Notification Appliance Design — Audibility and Candela Ratings

15 dB above ambient or 5 dB above the loudest 60-second sound; strobes by room size and the synchronization rule.

#66 FACP Standby Battery Calculation — 24 Hours Plus 5 Minutes

Total quiescent current for 24 h, plus full alarm current for 5 min, times a 1.2 ageing factor — that is the amp-hour size.

#67 Manual Call Point Placement per RA 9514 and NFPA 72

One at every exit, within 1.5 m of the door, no more than 60 m travel to reach one, 1.1–1.4 m mounting height.

#68 Fire Alarm Cable, Conduit, and Circuit Takeoff

Loop and NAC runs with drop and slack allowances, fire-rated cable where survivability is required, and EMT throughout.

#69 Conventional vs Addressable FDAS — Cost and Design Impact

Conventional is cheaper hardware but more wire and coarser location; addressable costs more per point but scales and pinpoints.

Painting

#70 Painting Takeoff per BS 6150 — Areas, Deductions, and Coats

Measure the surface, deduct openings over 0.5 m², multiply by the number of coats, then divide by coverage rate.

#71 Paint Coverage Rates and Estimating Litres per Coat

Theoretical spreading rate from volume solids and film thickness; practical rate after loss factors.

#72 ISO 12944 Corrosivity Categories and Coating Systems

C1 to CX sets the environment; the environment plus the durability class picks the primer / intermediate / topcoat stack and total DFT.

#73 Surface Preparation and Primer Selection by Substrate

The primer is chosen by what is underneath — plaster, concrete, wood, ferrous, or non-ferrous metal each need a different first coat.

#74 Interior vs Exterior Coating Systems — Spec and Quantity

Exterior systems add a masonry sealer, UV-stable finishes, and higher wastage — and often an elastomeric option for hairline cracks.

#75 Painting Labor Productivity and Crew-Hour Estimating

Labour is 40–60% of a painting bill. Estimate it in m² per painter-hour by surface and method, not as a flat percentage.

Estimating / BOQ

#76 Quantity Takeoff Principles — Order, Units, and Cross-Checks

Take off in construction sequence, measure net in standard units, and cross-check every quantity against a second number.

#77 Wastage and Allowance Factors by Material

Cut-and-fill offcuts, breakage, over-order minimums, and laps — each material has a defensible waste percentage.

#78 Unit Rate Build-Up — Material, Labor, Equipment, and Overhead

A unit rate is a small estimate: material + labour + plant + overhead + margin, per unit of finished work.

#79 Building and Maintaining a Material Price Database

Structure it by category and unit, date every price, keep a source, and update the volatile items monthly.

#80 Structuring a BOQ by Trade Section

Preliminaries, then substructure to finishes to external works — a consistent section order every bidder can follow.

#81 Preliminaries and General Requirements in a BOQ

The 8–15% of the bid that is not bricks and mortar — site management, temporary works, plant, and compliance.

#82 Estimate Classes — Conceptual, Preliminary, and Definitive

Class 5 to Class 1: as the design matures, the method changes and the accuracy range narrows from ±50% to ±10%.

#83 Price Escalation and Contingency in Construction Estimates

Escalation moves today’s prices to the construction midpoint; contingency covers risk. They are not the same line.

#84 The 12 Most Common Estimating Errors — And How to Catch Them

Unit mix-ups, missed scope, stale prices, and no cross-check — the errors that show up again and again, and the checks that catch them.

Project Management & Bidding

#85 Multi-Discipline BOQ Consolidation for a Whole Building

Each discipline estimates separately, then one consolidation reconciles interfaces, removes overlaps, and produces a single grand total.

#86 Comparing Subcontractor Bids — Scope, Spec, and Exclusions

The lowest number is rarely the lowest price. Normalise scope, specification, and exclusions before you compare.

#87 Site Overhead and General Conditions — What to Include

Supervision, temporary facilities, utilities, safety, equipment, permits, and insurance — itemised, time-related where it should be.

#88 Contingency vs Profit Markup — Keeping Them Separate

Contingency is the client’s money for risk; profit is your return for taking the job. Mixing them loses bids and loses arguments.

#89 Markup and VAT Math for a Philippine Construction Bid

Stack the components in order, apply profit as a margin (not a markup on cost), and add 12% VAT last — with the retention and CWT noted.

#90 Progress Billing and the Schedule of Values

Break the contract sum into billable line items, claim % complete each period, and track earned value to date against the balance.

#91 Change Order Pricing and Documentation

Price the add and the omit at contract rates where they exist, fair rates where they don’t, and log every one before proceeding.

#92 Conceptual Estimating by Building Type and Floor Area

Cost per square metre by building type and quality, adjusted for location, height, and site — a budget in an afternoon.

#93 Retention, Mobilization, and Payment Terms in Quotations

Advance payment, retention percentage and release, billing frequency, and payment period — the cashflow terms that decide whether a profitable job is also a survivable one.