How is rebar usually estimated?

Either by bar list (diameter × length × unit weight) or as a pounds-per-CY ratio from experience on similar structures.

Do I measure gross or net slab area?

Gross area, then deduct only where the drawings show openings large enough to matter to the pour.

Takeoff Guides

Concrete Takeoff Guide

Short answer

A concrete takeoff measures cubic yards of concrete by element type (footings, walls, slabs), square feet of formwork contact area, and pounds of reinforcing steel — each separated by mix design and application of a waste factor.

Concrete is priced three ways at once: material by the cubic yard, formwork by contact square foot, and reinforcement by weight. Miss any one of the three and the estimate is wrong even if the geometry is right.

The drawings to measure are the foundation plan, framing plans, sections, and the schedules — column, footing, and beam schedules carry the sizes the plan symbols point at.

What to measure

Footings — continuous and spread, by schedule type.
Slabs on grade — area times thickness, by mix and region.
Elevated slabs — area times thickness plus beams.
Walls — height times length times thickness.
Columns, pilasters, beams — by schedule type and count.
Formwork contact SF for every formed element.
Rebar pounds per element — or a justified % of volume.

Concrete takeoff units

Item	Unit	How measured
Concrete — footings, slabs, walls, columns	CY	Volume: L × W × D ÷ 27
Formwork	SF	Contact area of formed faces
Reinforcing steel	LB	Bar weight table × LF placed, or % of CY
Wire mesh / fiber	SF	Slab area covered
Vapor barrier, curing	SF	Slab area

Symbols and schedules

Foundation and framing plans use tags that resolve in the schedules — F-2 means nothing until the footing schedule gives its dimensions. Takeoff here is schedule-driven: measure counts and locations on the plans, then size from the schedule.

Calibrate before you measure

Structural sheets change scale between plans and details constantly. A footing measured on a 1/8" plan and a section drawn at 3/4" need separate calibrations — measure on the sheet whose scale you just verified, never assume it carried over.

Common mistakes

Counting a beam or column schedule line but missing its quantity multiplier.
Measuring slab area and forgetting the thickened-edge footings inside it.
Applying one waste factor to everything — pump loss, spillage, and over-excavation differ by element.
Forgetting formwork has two faces on walls.

Doing it in PDFDepth

AI Takeoff counts tagged elements and measures calibrated areas; Export Takeoff to Excel produces one row per measurement for pricing. For a whole structure set, the Master Takeoff Report aggregates every sheet into one workbook.