Takeoffs

Measuring a drawing so the number can be defended.

A quantity on a takeoff is a claim about a building, and an estimator who cannot answer "where did 1,240 SF come from?" cannot defend a bid. Everything in this guide exists to make that question answerable six months later.

1. Set the scale first

Nothing measures until the page is calibrated. SheetForge will not guess, and it will not quietly fall back to 1:1. An uncalibrated measurement reports as underived — a dash, not a number — because a zero would be indistinguishable from a real measurement of nothing.

There are three ways to set it, and they are not equally trustworthy.

Then check it. Pick Check a dimension, drag along a different printed dimension, and type what that one says. The answer is graded: within 1% the scale is right, within 5% draw it again, beyond that something is wrong — and where the error matches a mistake people actually make, it says which. A half-size plot, feet entered where inches were meant, metres where feet were meant.

This takes two seconds and it is the only thing standing between a mis-calibrated page and a bid built on numbers that are all wrong together. A wrong scale does not look wrong: every length is consistently out and every area is out by the square, and the drawing carries on looking exactly like a drawing.

Practise this first. The tutorial sheet that ships with SheetForge exists mostly for this step: page two prints a 144'-0" dimension whose geometry really is 144 feet, so you can calibrate against it and then check your answer against a second dimension the sheet also prints. Project → Open the tutorial sheet. Getting this wrong on a real drawing produces a confident wrong number, and nothing downstream will catch it for you.

Draw a known dimension — the strongest

Pick Calibrate, draw a line along something whose real length is printed on the sheet, and type that length. Use the printed graphic scale bar if there is one, or an overall dimension string.

This is the only method that survives re-plotting. A sheet whose title block says 1/8" = 1'-0" may well have been plotted to fit A3 for a meeting, and the graphic scale bar shrank with the drawing while the title block did not. The bar is the witness that still tells the truth.

If your hand-drawn calibration lands within 1.5% of a standard scale, SheetForge labels it as that scale — so 1/8" = 1'-0" shows as 1/8" = 1'-0", not as 0.111 ft/pt.

Choose a named preset — good, if the plot is true

1/4" = 1'-0", 1:100, and the rest. Fast and exact when the sheet was plotted at full size.

Let OCR read the title block — a suggestion, never a fact

If the sheet has been recognised, SheetForge can offer the scale it read. It arrives marked provisional and every quantity derived from it is flagged, until you confirm it. Confirming is one click; it is a separate click on purpose.

SheetForge never silently infers a measurement scale, and never presents an OCR-derived scale as verified. An unverified scale that quietly becomes authoritative is how a bid goes out wrong.

One scale per page — not per document

A plan sheet and the enlarged detail beside it are different scales. A document-wide factor produces confidently wrong numbers on half the set, and they look completely plausible. Calibrate each page you measure on.

Units

Set the unit when you calibrate: ft, in, m, mm. Imperial lengths render as feet and inches — 12'-6 1/2", not 12.54 ft — and typing accepts 12'-6", 6 1/2", 3/4", 300mm or 4 meters.

2. Measure

That third column is not decoration. A page-space area scales by the square of the scale factor: applying the factor once produces a number that looks like an area, is wrong by the whole scale factor, and passes every eyeball check. SheetForge applies the right exponent per measurement kind, and there is a test that says so.

Counts and angles need no scale at all, so they work on an uncalibrated page.

While you draw

• Snap to angle with Shift.
• Space places a point, Enter finishes, Backspace removes the last point.
• A running total shows as you go.
• A measurement is a markup like any other, so it carries a subject, a discipline, an assignee and a cost code. That is how it rolls up.

3. Bucket it

Put a cost code (the engine calls it trade) on each measurement, or a takeoff assembly: 03 30 00, 09 Finishes, Bid package 3. Then the roll-up groups by it, and the CSV lands in your estimate already sorted rather than as 400 loose numbers.

Labels stack on top for anything the cost code does not capture — level-4, phase-2, alternate.

4. If the scale was wrong

Re-calibrate the page. Every measurement on it re-derives.

This is the single most useful property of the takeoff and it is worth understanding why it works. A quantity is never stored as a bare number. It carries:

So fixing a wrong scale is fixing the scale — not redrawing eighty measurements. And if a calibration is removed, the quantities go back to underived rather than to zero: a visible state you can act on, instead of a plausible number that is wrong.

5. Where the scale came from

Each quantity displays its provenance, and a provisional flag when the scale behind it has not been confirmed by a human. Provisional numbers are meant to be visible: an unverified takeoff going into a bid is a commercial risk, and somebody should get the chance to notice.

Check before you export:

• Every page you measured on is calibrated.
• No calibration is still marked provisional.
• Detail pages carry their own scale, not the plan's.
• Areas are in the unit you think they are — ft² is not ft.
• Counts and angles are on the page you meant, even though they ignore scale.

6. Export the numbers

CSV or XLSX, from the takeoff panel. Each row carries what makes it defensible:

Anyone handed that spreadsheet can recompute every figure from the raw magnitude and the scale without opening SheetForge. That is what "defensible" means in practice.

Every export is written to the audit trail.

7. Worked example

A second-floor plan, ARCH D, printed 1/8" = 1'-0", and you need the slab area.

1. Calibrate. Draw along the overall dimension string. It reads 144'-0"; type 144'. SheetForge computes ≈ 0.1111 ft per PDF point and, being within 1.5% of a standard scale, labels the page 1/8" = 1'-0".
2. Sanity-check it. Measure a column bay you know is 30'-0". If it comes back 30'-0", the scale is right. If it comes back 15'-0", the sheet was plotted at half size and your calibration just saved the bid. Do this every time.
3. Measure the slab. Area tool, trace the perimeter, Enter. 12,480 SF.
4. Bucket it. Cost code 03 30 00, subject "L2 slab on metal deck", discipline structural.
5. Export. The CSV row carries raw_page_magnitude = 1010880 page units², the calibration id, verified = yes, and the revision and page it came from.

Six months later, in a dispute about the quantity: the row names Rev C of sheet S-201 page 4, the scale that was used, who confirmed it and when — and the audit trail shows nobody changed it since.

8. What this will not do for you

Stated plainly, because a takeoff tool that overclaims is worse than one that does less:

• No automatic quantity extraction. SheetForge does not read a drawing and tell you how many doors are on it. Automated measurement that has not been checked by a person is a number nobody can defend, and it is deliberately not in this version. See the roadmap for what is being considered and under what conditions.
• No model-based quantities. This measures drawings, not IFC models. Issues round-trip to the coordination model through BCF; quantities do not.
• No estimating. There is no cost database, no labour rate and no assembly pricing. The output is quantities, bucketed by cost code, for the estimating system you already have.
• Accuracy is bounded by the drawing. A measurement is exactly as good as the scale it was taken at and the drawing it was taken from. On a medium-resolution scan of an old drawing, that is a real limit and no amount of decimal places changes it.

Next

• Marking up drawings — the review workflow around the measurements
• Architecture — where measurement provenance is enforced, and how