Rebar area calculator: As for any bar group
Add bars by size and count to get total steel area, or pick a bar and spacing to get area per foot. Compare against a required area and see the weight, using ASTM A615 nominal values.
- Total As for bar groups
- Area per foot at spacing
- Compare to required As
- Weight per foot
1 · Bar groups Total As of a bar group
2 · Area per foot (slabs & walls)
3 · Check against required
Bar weights, diameters and areas: ASTM A615/A615M standard inch-pound bar sizes (also in the CRSI Manual of Standard Practice). 1 in² = 645.16 mm². This tool adds up nominal areas; it does not design reinforcement.
Live formula
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Copy these results, then add your approved sample files in the trial brief.
Substitutions, alternates and checks
Most takeoffs need pounds, not square inches. Steel area matters when the bar size changes: a value-engineering proposal to swap #5 at 12 in for #4 at 8 in, a fabricator who is out of a size, or an engineer's note that specifies a required area instead of a bar. In each case you need to show the alternate provides at least the same area before anyone will accept it, and you need the weight difference to price it.
- Group area. Σ count × nominal bar area. Three #8 bars provide 3 × 0.79 = 2.37 in².
- Area per foot. Bar area × 12 ÷ spacing. #5 at 12 in gives 0.31 in²/ft; #4 at 8 in gives 0.30 in²/ft.
- Weight per foot. Total linear weight of the group, useful for comparing alternates by cost.
- Required As. Enter the engineer's required area to see whether the selection meets it.
Areas from ASTM A615
| Bar | Diameter (in) | Area (in²) | Weight (lb/ft) |
|---|---|---|---|
| #3 | 0.375 | 0.11 | 0.376 |
| #4 | 0.500 | 0.20 | 0.668 |
| #5 | 0.625 | 0.31 | 1.043 |
| #6 | 0.750 | 0.44 | 1.502 |
| #7 | 0.875 | 0.60 | 2.044 |
| #8 | 1.000 | 0.79 | 2.670 |
| #9 | 1.128 | 1.00 | 3.400 |
| #10 | 1.270 | 1.27 | 4.303 |
| #11 | 1.410 | 1.56 | 5.313 |
Values per ASTM A615/A615M nominal dimensions.
Area equal, cost different
Smaller bars at tighter spacing can match area with similar weight but more pieces, more ties and more placing labor. Larger bars at wider spacing mean fewer pieces but may exceed maximum spacing limits. When you price an alternate, carry weight, piece count and placing hours together. The calculator gives the area and weight side; your crew history gives the labor.
RenderDraw's AI takeoff helps with the counting underneath: it proposes reinforcement callouts and element quantities from the plan set with their sources, so when you test an alternate you are changing a checked quantity, not re-measuring a set.
Rebar and concrete quantities you can trace back to the sheet.
RenderDraw's AI takeoff proposes counts, lengths and areas from structural drawings and schedules, keeps the source on every row, and holds uncertain items for estimator review.
- Footing, slab and wall schedules read in context. Quantities stay linked to the schedule and plan that produced them.
- Review queue sorted by confidence. Work the questionable items first.
- Addenda through the same review. Send the changed sheets back through takeoff and estimator review.
- Estimator approval before pricing. Laps, waste, accessories and labor stay with you.
Send one structural set
Include the foundation plan and schedules. Files stay private while RenderDraw assesses the request. No obligation.
RenderDraw does not publish accuracy percentages or time-saved claims. Test it on your own plan set.
Questions estimators ask.
What is the area of #5 rebar?
0.31 in² per bar (ASTM A615 nominal). #4 is 0.20 in² and #6 is 0.44 in².
How do you calculate rebar area per foot?
Multiply the single-bar area by 12 and divide by the spacing in inches. #5 at 12 in o.c. gives 0.31 in²/ft; #5 at 6 in gives 0.62 in²/ft.
How do I compare two rebar options?
Compare area per foot (or total As) first, then weight per foot for cost. The calculator shows both and the ratio to the required area.
Can I substitute bar sizes if the area is equal?
Only with the engineer's approval. Area is one requirement; spacing limits, development lengths and crack control also apply.
Does RenderDraw do rebar takeoffs?
RenderDraw's AI takeoff proposes reinforcement quantities with sources and flags for review. Request a free sample takeoff.
Fewer hours counting, more hours checking.
Send a structural set. RenderDraw proposes reinforcement quantities by element with the source sheet attached, and holds unclear callouts for review.
- Upload the plans, specs and schedules, plus an addendum if you have one.
- RenderDraw reviews the set and the scope you want tested.
- We follow up with extracted quantities, flagged items and next steps.