In our last column, we finished with the application of labor units. This month's article focuses on important modifications to the itemized estimating technique, including the two most popular techniques: assembly estimating and unit pricing.


Estimatic Corp. first popularized the assembly method in the 1950s. The company used the concept that virtually every type of electrical symbol used in construction drawings could be summarized as a specific list of materials. For example, the assembly for a common receptacle would include the receptacle, the finish plate, a box, a plaster ring, screws for fastening the box to the framing, a grounding pigtail, a couple of feet of No. 12 wire in the box, an average of two wire nuts and two ½-in. EMT connectors. Thus the assembly includes everything indicated by the duplex receptacle symbol on the plans.

This is typical of all assemblies. There could be thousands of assembly combinations with different types of receptacles with various types of finish plates and plaster rings. Even raceways can be broken down into assemblies. For example, three No. 12 THHN conductors in ½-in EMT, three No. 8s and one No. 10 in 1-in. EMT, etc.

When the estimator takes off a job, he or she counts all the symbols and raceways on the plans and then prices the list as assemblies (so many type XYZ assemblies, so many type ABC assemblies, etc.) Because all the assemblies are pre-priced and pre-labored, the counting and pricing of individual parts are mostly eliminated.

Many computer estimating systems will take assemblies, break them down into their individual parts and print out one complete bill of material.


The concept of unit pricing is very simple. Unit pricing establishes a set dollar amount to charge for each particular item or group of items identified by one symbol or name. For example, a customer will ask for the price of each receptacle. However, he doesn't want the price for the duplex receptacle alone, but the price for the receptacle, trim plate, box, ring, conduit or cable and labor. He wants a total price for each item that he can see and use, and he identifies it by one name — a receptacle.

Because of the convenience of unit pricing, it is widely used. With a good set of unit prices, an estimator can price a complete job by just counting the symbols on the plans and multiplying them by their unit prices to determine the selling price. This eliminates the long and difficult task of making an itemized, detailed estimate for each job.

The most important concept to understand about unit pricing is that a unit price includes everything, whether specifically expressed or not.

For example, we understand that the duplex receptacle unit contains items such as the box, trim plate, fasteners and raceway or cable; but what about the circuit breaker that must feed power to the receptacle? This must also be included in the unit if the price is to be accurate.

If we can remember to include every item that makes up the unit, we then have a complete unit that we can price and use with full confidence.

You should also include certain characteristics in your unit pricing calculations:

  • The cost of material and labor for an appropriate fastener with each strap.

  • Miscellaneous material and labor in each unit for as tape, wire lube, wire markers and testing.

  • The material cost of light fixtures or fans in the residential unit prices is usually omitted, as most homebuilders furnish these items.

  • Material and labor for No. 12 Romex (Type NM cable) is generally calculated at a 4 to 1 average ratio of No. 12/2 to No. 12/3.

  • Double switches are generally omitted for residential units because there is no significant cost difference between two switches and a double switch. For the commercial units, double switches are included, because there is a big savings in raceway.

  • The cost of the permit and other unusual expenses when totaling your estimate; and watch for exceptionally long runs or heavy equipment, which must be compensated for.

Reprinted with permission from NFPA Successful Electrical Contracting. Copyright 2001 National Fire Protection Association, Quincy, Mass., 02269. This reprinted material is not the referenced subject, which is represented only by the standard in its entirety. To purchase a copy of NFPA's Successful Electrical Contracting, go to NFPA's online catalog at