G'day,

My estimating graph has undergone further refinement, so here is it.

Basically, any fabricator or builder worth anything will have a quantity surveyor go over the tender documents, so they will know exactly (or almost exactly) the tonneage of steel involved. They will also know the total linear metres of steel involved. If they don't and you have the drawings to quote off, you can measure and scale off physical drawings, or use a program like Bluebeam PDF Revu (CAD Edition) and actually measure off the stick drawing that are provided. Using the total tonneage and the total linear metres you have been given or provided to you, you come up with an average kg/m for the job.

You then go to the graph and establish which range you fall into and this gives you the hours per tonne to prepare the details (model and details). You then multiply that figure by whatever your hourly rate might be to quote on a $/tonne basis.

If you are not given a tonneage because the builder wants to catch you out, you can guestimate an average kg/m and go from there.

In any case, you should include a clause in your quote that is effectively a "rise and fall" clause to cover increases or decreases in tonneage, and even here specify that the tonneage is based on calculated tonneage using a steel bulk density of 7.85 tonnes/cubic metre.

Summarising the graph, it goes like this:

Avg. kg/m^3 ................. h/t

---------------------------------------

> 80 ........................... 4

70 - 80 ........................ 5

60 - 70 ........................ 6.25

50 - 60 ........................ 7.25

40 - 50 ........................ 8.5

30 - 40 ........................ 9.5

20 - 30 ........................ 10.75

10 - 20 ........................ 11.75

0 - 10 ......................... 13

You can decide what to do if the value falls on a boundary

Anyhow, it is a method of getting consistent costs for detailing.