Grid counts and linear steel estimate
The linear total describes one grid layer. Stock bars are an aggregate length estimate and can be too low when offcuts cannot supply required lengths. Draw a cutting list before placing an order.
For the concrete quantity in the slab, use the Concrete Calculator with the intended slab dimensions and thickness.
The formula
Cover is converted from inches to feet and removed from both ends. Dividing the clear transverse span into enough intervals keeps the equalized spacing at or below the specified maximum. Stock quantity uses aggregate length with waste, not individual cut optimization.
Worked example
For a 20 by 10 ft slab with 2 in cover and 12 in maximum spacing, clear dimensions are 19.6667 by 9.6667 ft. The grid has 11 lengthwise and 21 crosswise bars, totaling 419.3333 ft. Adding 10% and dividing by 20 ft stock gives 24 bars by aggregate length.
How to use this calculator
- Enter slab length, slab width using the units shown.
- Set edge cover, maximum grid spacing, stock bar length, additional length allowance.
- Calculate and review grid bar length alongside the supporting quantities.
Specified spacing and edge cover
Use the reinforcement spacing, bar size, and cover from the approved design. The calculator divides each clear span evenly, including a bar at each edge of the grid. It does not determine whether a slab needs reinforcement or whether the proposed layout satisfies loading, crack control, exposure, or placement requirements.
Laps and cut schedules
Long members may need lap splices, hooks, bends, supports, or a second reinforcement mat. Those details add steel beyond straight lengths. Aggregate stock rounding cannot model the pieces cut from each bar. Where the cut length is near the stock length, check every piece individually and allow for specified overlap and fabrication losses.
Assumptions & limitations
What this calculation assumes
- One orthogonal layer of straight bars is counted.
What to keep in mind
- No bar size, lap length, anchorage, strength, or cutting optimization is selected.
Common questions
Why is there one extra bar?
The count is the number of spacing intervals plus a bar at each end. A ten-interval span therefore uses eleven bars.
Can I double this for two mats?
Double only the grid quantity if both mats use the same layout, then add their distinct supports, laps, and details.
Are stock bars optimized for cutting?
No. The displayed count is based on aggregate length. A cut schedule can need more stock bars when offcuts do not fit the required pieces.
Sources & further reading
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