Free tool · Takeoff
Rebar Weight and Count Calculator
Enter the two sides of a slab, wall or mat, the bar size and the spacing, and the calculator counts the bars both ways, adds the splices for bars longer than your stock length, and totals the length and weight. Add footing bars, dowels or extras as individual lines, then set the waste and the stock bar length to see how many bars to order.
The numbers stay in your browser: we do not store or receive them.
Bar grids: slab, wall, mat or footing
Enter the two sides, the bar size and the spacing. Bars run both ways. Leave a grid blank to skip it.
Individual bars: footings, dowels, stirrups, extras
Ordering
Weight
807 lb
0.40 short tons, before waste
Order with 5.0% waste
848 lb
0.42 short tons
Stock bars to order
64
20 ft lengths, 50 bars placed, 20 splices
| Bar | lb/ft | Bars placed | Length (ft) | Weight (lb) | Stock bars |
|---|---|---|---|---|---|
| #4 | 0.668 | 50 | 1,208.3 | 807 | 64 |
How the bars are counted
Bars across a span = (span − 2 × cover) ÷ spacing, rounded down, plus one for the last bar. A 30 ft side with 3 in cover and bars at 12 in on center takes (360 − 6) ÷ 12 = 29.5, which is 29, plus 1 = 30 bars.
Bar length = the side − 2 × cover. Bars run both ways, so one grid gives two sets of bars: those running along side 1 and those running along side 2.
Splices. A bar longer than the stock length is lapped. The lap is a multiple of the bar diameter that you enter (it should come from your drawings), and each splice adds one lap length of bar.
Weight of the bars
Weights are the standard ASTM A615 nominal weights per foot: #3 is 0.376 lb/ft, #4 is 0.668, #5 is 1.043, #6 is 1.502, #7 is 2.044, #8 is 2.670, #9 is 3.400, #10 is 4.303, #11 is 5.313, #14 is 7.650 and #18 is 13.600. Up to #8 the bar number is the diameter in eighths of an inch, so a #5 bar is 5/8 in. Tons are short tons of 2,000 lb.
A worked example
A 20 ft by 30 ft slab with #4 bars at 12 in on center each way, 3 in of cover, one mat and 20 ft stock bars needs 30 bars of 19.5 ft and 20 bars of 29.5 ft. The long bars are lapped once (a 20 in lap at 40 bar diameters), so each uses 31.2 ft. That is 50 bars placed, 1,208 ft of bar and 807 lb, or about 0.40 ton.
With 5 percent waste the order is about 848 lb, which is 64 stock bars of 20 ft.
What this does not do
It does not design the reinforcing: the bar size, spacing, cover and lap lengths come from your structural drawings and the code. It does not add hooks, bends, stirrup lengths, chairs, tie wire or the extra bars at openings and corners, so list those as individual bars. The stock bar count is the total length divided by the stock length, not a cutting plan, so leftovers from cutting are covered only by the waste percent. Check lengths and weights with your supplier.
FAQ
How do I figure rebar for a slab?
Count the bars each way from the spacing, multiply by the length of each, add the splices, and multiply the total length by the weight per foot of the bar size. The calculator does all of that from the two sides, the spacing and the cover.
How much waste should I add?
Many estimators use about 5 percent for cutting and leftovers on straight bars, and more on jobs with lots of short cut pieces. It depends on your layout, so the box is yours to change.
What is a lap splice?
It is where two bars overlap so that they act as one. The required length is set by the structural drawings and the code, often as a number of bar diameters, so enter the value from your plans.
What does the bar number mean?
For #3 through #8 the number is the diameter in eighths of an inch, so #4 is 1/2 in and #8 is 1 in. Larger sizes follow the ASTM table instead of that rule.
Does this work for walls and footings?
Yes. A wall is the same grid with the height as side 2. For a continuous footing, use the individual bar lines for the long bars and a grid or more lines for the cross bars.
Is anything I type saved?
No. The calculation runs in your browser and nothing is stored or sent to us.
Pricing the whole pour? PoPs Estimating measures slabs, footings and rebar from your plans and keeps the quantities tied to the bid.
Questions?
Ask us anything about PoPs Suite, pricing, or running a construction company. A real person answers, usually within a business day.