Rebar Basics
Rebar Size Chart: What Each Bar Number Means
A quick reference to US bar sizes, their diameters and weights — where each one usually shows up on a commercial job, and how to turn a drawing into tonnage.
US reinforcing bar is numbered in eighths of an inch. A #5 bar is 5/8 inch in diameter, a #8 is one inch. Once you know that, the chart mostly reads itself.
The diameter quoted is a nominal diameter — the diameter of a plain round bar of the same weight per foot. A real deformed bar has ribs, so it measures slightly larger across them. That distinction matters when checking bar against a list with callipers, and it matters when working out whether a congested detail will physically fit.
The imperial sizes
- #3 — 0.375 in, 0.376 lb/ft. Ties, stirrups, light slab and wall mesh work.
- #4 — 0.500 in, 0.668 lb/ft. Residential and light commercial slabs, walls, small footings.
- #5 — 0.625 in, 1.043 lb/ft. Very common in commercial slabs, walls and footings.
- #6 — 0.750 in, 1.502 lb/ft. Heavier footings, columns, beams.
- #7 — 0.875 in, 2.044 lb/ft. Beams, columns, transfer elements.
- #8 — 1.000 in, 2.670 lb/ft. Column verticals, heavy beams.
- #9 — 1.128 in, 3.400 lb/ft. Heavy columns, mats.
- #10 — 1.270 in, 4.303 lb/ft. Heavy foundations and cores.
- #11 — 1.410 in, 5.313 lb/ft. High-rise columns, deep mats.
- #14 and #18 — 1.693 in and 2.257 in. Large infrastructure and very heavy foundation work.
Note that the neat eighths break down after #11 — #14 and #18 are sized by area, not by diameter, which is why the pattern stops.
The reason is historical and practical. #14 and #18 correspond to bars of 1.5 and 2.0 square inches of cross-section respectively — round numbers in area, not in diameter — because at that size the quantity an engineer cares about is area, and the bars exist for elements where area is the binding constraint. There is no #12, #13, #15, #16 or #17, and asking for one is a good way to identify a drawing that has not been checked.
Why weight per foot is the useful column
Weight per foot is the number that turns a placement drawing into tonnage. Total linear feet of each size, times the pounds per foot, gives the weight — which drives the price, the delivery schedule, and how much of it the crew has to move by hand.
That last part matters more than people expect. A mat of #9 is a different physical job from the same geometry in #5, and the crew size and lift plan should reflect it.
Worked through: a bay needing 4,000 linear feet of #5 is 4,000 × 1.043 = 4,172 lb, just over two tons. The same bay redetailed in #8 at wider spacing to give a similar area might be 1,800 linear feet at 2.670 = 4,806 lb — comparable weight, less than half the pieces, and a completely different day for the crew. Fewer, heavier bars need mechanical handling; more, lighter bars need more ties and more hands.
This is why tonnage alone is a poor basis for pricing. Two packages of identical weight with different size mixes are different contracts.
Reading a bar
Every bar carries rolled markings: producer mill, size number, a letter or symbol for the steel type, and a grade mark. On a jobsite that is how a bundle gets verified against the bar list before anything is placed, and it is the first thing an inspector looks at.
The grade mark is the one worth checking hardest, because a size error is usually obvious by eye and a grade error is not. The markings survive mud and weather, which is the point of rolling them in rather than painting them on.
Size, bend and the shapes on a bar list
Bar size governs more than weight. It sets the minimum diameter a bar can be bent around without damaging the steel, and that minimum rises with size and with grade.
This is why a shape that works in #4 may be impossible in #9 — the bend radius required makes the leg lengths impractical, or the bar will not fit the element once bent. Impossible bends are one of the standard findings in a constructability review, and they are cheap to fix while the drawings are live and expensive once fabrication has started.
Size also drives lap and development length, which scale with bar diameter. A splice in #9 takes much more room than a splice in #5, which is why large-bar details get congested precisely where bars overlap.
Where each size tends to appear, and why
#3 and #4 do the distributed work: ties, stirrups, temperature and shrinkage steel, light slabs. Small enough to bend easily and handle by hand, and there are a great many of them.
#5 and #6 are the commercial workhorses — slabs, walls, footings — because they carry useful area at a size one person can still place efficiently.
#7 through #9 are element steel: beams, columns, mats. Heavy enough that handling changes character, and where you start seeing mechanical placement.
#10 and #11 are for the heavily loaded: high-rise columns, deep foundations, cores.
#14 and #18 are infrastructure and very heavy foundation bar, where area is everything and placement is a crane operation.
Metric, and why it occasionally appears
Soft-metric designations — #16 for what was #5, #25 for what was #8 — appear on some drawings and on mill certificates, and they describe the same bars in millimetres of nominal diameter rather than eighths of an inch. They are not different products.
The confusion they cause is real, though: a "#16" on a drawing is a metric #5 and not an imperial bar between #14 and #18, which do not exist as a sequence. Where a set mixes conventions, it is worth resolving in the submittal rather than on the deck.
Turning the chart into a number
Estimating quantity from a drawing is the chart's main job: count the bars per element, measure their lengths including hooks and laps, multiply by weight per foot, and total by size — because the size mix, not just the total, is what a fabricator prices and what a crew has to lift.
If you have a set and want the takeoff and the size mix read properly before it is priced, that is a conversation worth having.