Anatomy of a fabrication quotation
A fabrication quotation has four lines that matter: structural steel in kilograms, treads in kilograms, handrail in metres, shop labour in hours. On our sample quotation those lines total RM 7,025 at demonstration rates — and every one of them traces back to a single computation. This article walks the trace, line by line, and shows how to tell a traceable quotation from one copied off the last job.
Four lines: 260 kg, 289 kg, 12.7 m, 29 hours
The sample quotation on this page — VT-DEMO-Q-001, a steel access staircase with a 3.00 m rise and 1.00 m clear width — carries four lines. Structural steel (stringers, landing frame, kickplate): 260 kg, RM 2,033. Treads and landing plate in 6 mm checker plate: 289 kg, RM 2,459. Handrail in 42 mm tube: 12.7 m, RM 599. Shop labour for fabrication and welding: 29 hours, RM 1,934. Total: RM 7,025, at demonstration rates with a 15% margin.
The ringgit figures are the least interesting column — they are demonstration rates from our own estimating engine, not an offer. Look instead at the basis column. Every line is priced from a physical quantity: kilograms, metres, hours. And none of those quantities was typed in. Each one is the output of a computation that starts from two inputs — the rise and the width — and can be followed all the way down. That trail is what this article walks.
Where the 260 kg of steel comes from
Start at the geometry. A 3.00 m floor-to-floor rise divided by a maximum riser of 180 mm forces 17 risers, so each riser is 176 mm. The comfort rule 620 − 2R sets the going at 267 mm, and the checks pass: 2R + G lands at 619 mm, inside the 550–700 band, and the pitch works out to 33.5°, under the 38° limit. Seventeen risers will not fit in one flight, so the stair becomes two flights — nine risers and eight — with one landing.
The geometry then sizes the members. The longer flight needs a stringer spanning 2.66 m; PFC 150×75, with a span capacity of 3.20 m at 17.9 kg/m, is the lightest section that passes, so it is selected and PFC 200×75 is noted as not required. Four stringers across two flights come to 10 m of channel — 179 kg. Add the landing frame and kickplate and you have line 1's 260 kg. Nothing was keyed in by hand; the masses come from published section tables.
The BOM cross-check: 587 kg both ways
The going does not stay inside the calculation sheet — 267 mm reappears on the bill of materials as the tread plate size, 267 × 1000 mm, fifteen pieces, because seventeen risers over two flights leaves fifteen treads plus a landing. Treads come to 234 kg, the landing to 136 kg, the handrail to 12.7 m of 42 mm tube at 38 kg. The BOM totals 587 kg — and the quotation's two steel lines plus the handrail tube sum to exactly the same figure, because the BOM and the quotation are one computation, not two documents someone has to reconcile at the end of the week.
29 shop hours, built up from 14.4 m of weld
Labour is where copied quotations are weakest — usually a gut figure, or a flat percentage of material. On this quotation it is a derived quantity like the others. The weld run — tread welds, flight joints, rail stitching — measures 14.4 m. Apply a weld rate, add handling time scaled by the 587 kg, add tread fit-up, and the labour line reads 29 hours: RM 1,934 at the demonstration rate. Because the hours are computed from the geometry, they move when the geometry moves — which is exactly what a copied labour figure cannot do.
Change the rise to 3.2 m and watch both documents
The real test of any quotation is the first revision, because clients revise. Change the rise from 3.00 m to 3.2 m in a copied workbook and count the manual edits: the riser count becomes 18, so the tread count changes, so the plate weight changes, so the weld run changes, so the hours change — four lines and a total to re-type on the quotation, and again on the BOM. Miss one and the two documents quietly disagree. Nobody notices until the shop cuts steel against the wrong number.
In the traceable version there is nothing to re-type. The rise is an input; the geometry, member selection, weights, weld run, hours and prices are all downstream of it, so all four lines re-solve together — the sample regenerates in 0.2 seconds. That is what traceable means in practice: not tidy formatting, but a single computation standing behind every number, so a revision is a new input rather than an afternoon of editing.
Run the trace on your own last quotation
Pick any line on the last quotation your firm sent and ask three questions. Where did this number come from — a computation, or the last similar job? Could anyone besides the senior estimator reproduce it from the inputs? And if the client moves one dimension, how many cells must be edited by hand before the quotation and the BOM agree again? A traceable quotation survives all three questions. A copied one usually fails the first.
We hold our own work to the same standard. Acceptance on any estimating build we deliver is the Re-quote Test: twenty of your past jobs re-computed through the new tool, against a tolerance agreed in writing before the build starts. Your costing workbook is the specification — it holds years of your firm's method — and the first deliverable is a map of what it computes and where it is fragile. Bring the workbook; the trace starts there.
Start here
Bring the workbook.
The workflow review is free: bring your last quotation and the workbook behind it, and we will show you exactly where the trace holds and where it breaks.