Rebar Size and Weight Chart (#3 to #11) with Lap and Cover Rules

Rebar size chart, #3 through #11

These are the same values the rebar weight calculator uses. Weight depends on bar size only. A Grade 40 bar and a Grade 60 bar of the same size weigh the same per foot.

Nominal diameter is the diameter of a plain round bar with the same weight per foot as the deformed bar. A caliper reading across the ribs is larger than the table value.

What the bar number means

For #3 through #8, the number is the nominal diameter in eighths of an inch. A #3 is 3/8 in., a #4 is 1/2 in., and a #8 is 1 in. The pattern is exact through #8.

Above #8 the diameters are 1.128, 1.270, and 1.410 in., not the 1.125, 1.250, and 1.375 in. the pattern would give. Those three sizes carry the cross-section areas of the older 1 in., 1-1/8 in., and 1-1/4 in. square bars, and the numbers stayed.

Weight follows area, not the bar number. A #8 has twice the diameter of a #4 and weighs four times as much per foot (2.670 lb against 0.668 lb). A #4 weighs 1.78 times a #3, and a #5 weighs 1.56 times a #4. Moving up one size on a large job changes the tonnage more than the bar number suggests.

Weight per bar and bars per ton

To turn a takeoff in linear feet into an order, multiply the footage by the weight per foot. Rebar is commonly stocked in 20 ft lengths. Longer stock and cut-to-length service depend on the supplier, so confirm both before laying out a job around one length.

Weight of a slab grid per 100 sq ft

A two-way grid has 12 divided by the spacing in feet of bar per square foot in each direction. At 12 in. on center that is 1 ft of bar per direction per square foot, or 200 ft of bar in 100 sq ft. A #4 at 0.668 lb per foot then gives 133.6 lb.

Steel area per foot of slab width is what the engineer designs for. A #4 at 12 in. gives 0.200 sq in. per foot. A #5 at 18 in. gives 0.207 sq in. per foot, which is nearly the same area with a third fewer bars to place and tie. The #5 grid also weighs 139.1 lb per 100 sq ft against 133.6 lb, about 4 percent more. Only the engineer of record can approve a substitution like this.

Lap splice lengths

A lap splice overlaps two bars so they carry load together. ACI 318 derives the lap from the development length of the bar, which depends on bar size, steel grade, concrete strength, cover, bar spacing, and coating. ACI 318 also sets a 12 in. minimum for tension lap splices.

The calculator uses 40 bar diameters, rounded to the nearest inch, a common estimating figure for Grade 60 bars.

For estimating, each splice adds one lap length to the bar. A #4 splice adds 20 in., or 1.7 ft, of steel to the order.

Concrete cover

Cover is the distance from the bar surface to the nearest concrete face. ACI 318 sets minimums by exposure. The figures below apply to normal-weight, nonprestressed, cast-in-place concrete.

Which row applies to a slab on grade depends on the base (bare soil, gravel, or a vapor retarder) and on the engineer's notes, so read the notes instead of picking a row. Chairs and bolsters hold the steel at the specified height during the pour. A mat that lies on the subgrade has no cover on the bottom, and the concrete does not lift it into position.

Worked example: 20 ft by 24 ft slab, #4 at 12 in. each way

1. Edge clearance is 3 in. on each side, so the reinforced area is 23.5 ft by 19.5 ft (24 minus 0.5, and 20 minus 0.5).
2. Bars along the 24 ft direction: floor(19.5 / 1.0) + 1 = 20 bars at 23.5 ft, which is 470 ft.
3. Bars across: floor(23.5 / 1.0) + 1 = 24 bars at 19.5 ft, which is 468 ft.
4. Net length is 938 ft. At 0.668 lb per foot that is 626.6 lb.
5. Adding 10 percent waste gives 1,031.8 ft and 689.2 lb, or 0.345 ton. The calculator returns these figures for the same inputs.

Cross-check with 20 ft stock. The 19.5 ft bars fit in one stick each, so 24 sticks. The 23.5 ft bars do not. Each needs a 20 ft bar plus a short piece of 3.5 ft plus a 20 in. lap, or 5.17 ft. Three short pieces come out of one stick (3 x 5.17 = 15.5 ft), so 20 pieces need 7 sticks.

The total is 24 + 20 + 7 = 51 sticks, or 1,020 ft and 681 lb. The net figure of 626.6 lb understates that order by about 9 percent. The calculator's 10 percent allowance lands within about 1 percent of the stick count for this layout. A layout whose offcuts cannot be reused would waste more, so count sticks when the layout is unusual.

How to order and what to check on delivery

• Order by size, length, and grade. Use total weight as a cross-check. Bent bars, hooks, and stirrups come from a bar list or shop drawing, not from a grid takeoff.
• Confirm the unit on the quote. Suppliers may quote by the pound, hundredweight (100 lb), or ton. A short ton is 2,000 lb. A metric tonne is 2,204.6 lb, which is 10.2 percent more steel for the same count.
• Ask whether billing uses table weight or scale weight. The two can differ slightly, so settle it before the order is placed.
• Read the mill marks. ASTM bars are rolled with marks for the producer, bar size, type of steel, and grade. Compare them with the tag and the order.
• Buy tie wire and chairs separately. The calculator counts bar steel only. Chair height sets bottom cover.

For slab volume and truck loads on the same job, see the concrete yardage chart. For how much extra to add on any material, see the material waste guide.

Common mistakes

• Counting spaces instead of bars. A 20 ft run at 12 in. spacing has 21 bar positions when bars sit on both edges. Count floor(span / spacing) + 1 after subtracting the edge clearance.
• Ordering net footage. Laps and cutoffs added about 9 percent in the worked example above. A takeoff with no allowance runs short.
• Mixing short tons and tonnes. A tonnage read in the wrong unit is off by 10.2 percent. Write the unit next to every weight on the order.
• Swapping sizes to save money. A smaller bar at closer spacing can match the steel area and still cost more in labor and weight. The substitution needs the engineer's approval.
• Setting the mat on the ground. Without chairs, bars sit on the subgrade and end up with no bottom cover.

Frequently asked questions