Rebar calculator for spread footings
Enter the footing size, cover, bar size and spacing each way. The calculator counts bars, adds hooks, totals linear feet and weight using ASTM A615 nominal weights, and tells you how many stock lengths to order.
- Bars each way
- Cover and hooks
- ASTM A615 weights
- Stock bar count
1 · Footing
2 · Bottom mat
3 · Top mat (optional)
4 · Order
Bar weights, diameters and areas: ASTM A615/A615M standard inch-pound bar sizes (also in the CRSI Manual of Standard Practice). Cover default per ACI 318 (3 in for concrete cast against and permanently exposed to earth); confirm with your structural notes. Bar counts round up so spacing never exceeds the maximum shown.
Weight by mat
Live formula
Save your results
Copy these results, then add your approved sample files in the trial brief.
Spacing, cover and the extra bar
Footing rebar is a mat of bars running each way. The number of bars in one direction is the clear width available for bars divided by the spacing, plus one, because a run of bars at 12 in on center across 6 ft of clear width has seven bars, not six. That "plus one" is the most common source of short orders on footing-heavy jobs.
- Clear width. Footing dimension minus cover on both sides. Footings cast against earth commonly use 3 in cover per ACI 318; confirm on the drawings.
- Bar length. Footing dimension minus cover at both ends, plus hooks if the detail shows them.
- Each way. Bars in the long direction are counted across the short dimension, and the other way around. Square footings with equal spacing have the same count each way.
- Top mats. Some footings carry a top mat as well. Enter it as a second footing type or double the count.
The math the calculator runs
| Bar | Diameter (in) | Weight (lb/ft) |
|---|---|---|
| #4 | 0.500 | 0.668 |
| #5 | 0.625 | 1.043 |
| #6 | 0.750 | 1.502 |
| #7 | 0.875 | 2.044 |
| #8 | 1.000 | 2.670 |
Nominal dimensions and weights per ASTM A615/A615M. Hook lengths depend on bar size and hook type per ACI 318 and the CRSI Manual of Standard Practice; enter the length from your detail.
Schedules, marks and counts
A footing schedule might have a dozen types, each with its own size, bar and spacing, and each used a different number of times on the plan. The calculator handles one type at a time. The real work on a footing-heavy job is matching every mark on the foundation plan to the schedule, counting each, and spotting the footing that appears on the plan but not in the schedule. Count marks twice, once from the plan and once from the grid, before you trust the total.
That counting is exactly what RenderDraw's AI takeoff is built to help with. It reads the foundation plan and the schedule together, proposes the counts and sizes with the source sheet attached, and holds anything ambiguous for your review instead of guessing.
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.
How do you calculate rebar for a footing?
For each direction, divide the clear width (footing size minus cover on both sides) by the spacing, round down, and add one bar. Multiply by the bar length (footing size minus cover, plus hooks). Total the linear feet and multiply by the ASTM A615 weight per foot.
What cover is used for footing rebar?
Concrete cast against and permanently exposed to earth commonly requires 3 in of cover under ACI 318. The drawings and specs govern, and the cover field is editable.
How much does #5 rebar weigh per foot?
1.043 lb/ft per ASTM A615. #4 is 0.668 lb/ft and #6 is 1.502 lb/ft.
How many 20 ft bars do I need?
The calculator nests the cut lengths into your stock length and counts stock bars. It does not optimize across footing types; for a full cut list, combine types in your fabricator's software.
Can RenderDraw do a rebar takeoff?
RenderDraw's AI takeoff reads schedules, plans and details to propose rebar quantities with sources and flags. Get a free sample takeoff.
Footing schedules, read for you.
Send a foundation plan set. RenderDraw ties footing marks to the schedule, proposes sizes and counts with their source, and flags any mark it could not match.
- 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.