5 rebar tonnage mistakes that cost concrete contractors money

Most rebar misses aren't bar size errors. They're geometry errors hidden inside well-meaning spreadsheet formulas.

Rebar is the line item that separates the contractor who knows their numbers from the one who hopes. Here are the five misses we see most often when we audit a contractor's spreadsheet bid.

Lap splices add 30–60 bar diameters per splice. A 60' wall with #5 horizontal at 16" OC isn't 45 bars × 60'. It's 45 bars × 60', plus splice laps, plus corner bars, plus dowels.

A 50' × 100' slab with #4 at 18" OC each way isn't (50 × 100) × some lb/SF factor. It's (50 ÷ 1.5) × 100 ft of bar one way, plus (100 ÷ 1.5) × 50 ft of bar the other way. The unit math matters.

A 24" × 24" column with #4 ties at 4" OC at the ends and 8" OC in the middle is two tie-spacing schedules. If your formula has one tie spacing, your tonnage is off by 12–18%.

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