Fe500 vs Fe550 TMT Bars: Difference, Strength and Which to Use
Fe500 vs Fe550 TMT bars: the number is the minimum yield strength in N/mm² under IS 1786: Fe500 bars yield at 500 N/mm² or more, Fe550 at 550 N/mm² or more. Fe550 is about 10% stronger, so a design can sometimes use less steel, but it stretches less before breaking: its minimum elongation is 10% against 12% for Fe500. The “D” versions (Fe500D, Fe550D) have tighter chemistry and higher ductility, which is why they are preferred in earthquake zones. For most Indian houses, Fe500 or Fe500D is the usual choice. Use the grade your structural engineer specifies.
When you buy sariya for a house, the dealer will ask which grade you want, and prices differ between Fe500, Fe500D and Fe550D. The grade decides how strong the bar is, how much it can bend before breaking, and even how long the laps must be. This guide explains the grades in plain terms, the IS 1786 values behind them, and how to check what you are buying.
Last updated: 24 October 2026
Fe500 vs Fe550: quick comparison
| Property (IS 1786 minimum) | Fe500 | Fe500D | Fe550 | Fe550D |
|---|---|---|---|---|
| Yield strength (0.2% proof), N/mm² | 500 | 500 | 550 | 550 |
| Tensile strength, N/mm² | 545 | 565 | 585 | 600 |
| Tensile strength above actual yield | 8% | 10% | 6% | 8% |
| Elongation, % | 12 | 16 | 10 | 14.5 |
| Chemistry limits (carbon, sulphur, phosphorus) | Standard | Tighter | Standard | Tighter |
| Typical use | General RCC in houses | Houses and buildings in seismic zones | Larger structures where less steel area helps | Larger structures in seismic zones |
IS 1786 also covers Fe415, Fe415D, Fe600 and “S” grades for special uses. Fe415 was the common grade for years; most house construction now uses Fe500 or Fe500D.
What “Fe500” and “TMT” mean
Fe is the chemical symbol for iron, and the number is the minimum yield strength in N/mm². Yield strength is the stress at which steel stops springing back and starts to stretch permanently. Structural design uses this value, so a higher grade lets the engineer count on more strength from each bar.
TMT stands for thermo-mechanically treated. Hot-rolled bars are sprayed with water as they leave the mill, which hardens the outer rim, and the heat still in the core then tempers it. The result is a hard, strong surface with a softer, ductile core: strong enough for design, and able to bend without cracking. The ribs rolled onto the surface help the bar grip the concrete; see how RCC works.
Strength vs ductility: why the “D” grades matter
Strength is how much load a bar can take; ductility is how much it can stretch and bend before it breaks. In an earthquake or overload, ductile steel bends visibly and gives warning, while brittle steel snaps. That is why the stronger Fe550 has a lower minimum elongation than Fe500, and why the D grades exist: they keep high strength but add ductility through tighter chemistry and a larger gap between tensile and yield strength.
IS 13920, the code for earthquake-resistant detailing, asks for high-strength deformed bars of grade Fe550D or lower with elongation above 14.5%. In practice, D grades such as Fe500D are the common choice for houses in seismic zones III, IV and V, which cover a large part of India.
Is Fe550 better than Fe500?
Not automatically. A higher grade only saves steel if the structure is designed for it. Points to know:
- You cannot swap grades on site. If the drawing is designed for Fe500, using Fe550 bars of the same size and number adds strength but does not reduce the steel. Using fewer Fe550 bars needs the engineer to redesign.
- Laps and anchorage get longer. The required development length in IS 456 increases with the steel’s design stress, so higher-grade bars need longer laps and anchorage. These must be detailed on the drawing.
- Ductility is lower for plain Fe550 than for Fe500, which matters in seismic zones.
- For a typical house with moderate spans and loads, the steel saving from Fe550 is small. Fe500 or Fe500D is the common, well-understood choice.
Bar sizes and weight
TMT bars are sold by weight but specified by diameter. The weight per metre is approximately d² ÷ 162 kg, where d is the diameter in mm. The grade does not change the weight; a 12 mm Fe500 bar and a 12 mm Fe550 bar weigh the same.
| Diameter | Weight per metre | Weight of a 12 m bar | Common use in houses |
|---|---|---|---|
| 8 mm | 0.395 kg | 4.74 kg | Stirrups, column ties, slab distribution bars |
| 10 mm | 0.617 kg | 7.40 kg | Slab main bars, stirrups |
| 12 mm | 0.889 kg | 10.67 kg | Beams, columns, footings |
| 16 mm | 1.580 kg | 18.96 kg | Columns and beams |
| 20 mm | 2.469 kg | 29.63 kg | Heavier columns and beams |
| 25 mm | 3.858 kg | 46.30 kg | Large columns, larger structures |
To work out steel weight for a job from the bar schedule, use the steel weight calculator.
How to check TMT bars when buying
- Grade and brand marking: genuine bars carry the manufacturer’s mark and grade rolled onto the bar at intervals.
- BIS certification: bars should be certified to IS 1786; ask for the licence details.
- Mill test certificate (MTC): ask for the certificate for the heat or batch you receive. It lists yield strength, tensile strength, elongation and chemistry; compare them with the table above.
- Weight check: weigh a few bars and compare with d² ÷ 162 per metre. Bars much lighter than this are undersized.
- Visual check: uniform ribs, no cracks, deep rust scale or bends from careless handling. Light surface rust is normal; flaky rust is not.
- Storage on site: keep bars off the ground on supports, covered, and separated by diameter and grade.
Hindi terms used on site
Reinforcement bars are सरिया (sariya), often “TMT sariya”. Sizes are given in mm, for example “barah mm ka sariya” (12 mm bar), though older site speech also uses सूत (soot), a unit of about ⅛ inch. Grades are said as written: “Fe 500” or “500 D”. A bundle of bars is a बंडल (bundle), and the bar bending schedule is called the BBS.
FAQ
What is the difference between Fe500 and Fe550 TMT bars?
Fe550 has a higher minimum yield strength (550 vs 500 N/mm²) but a lower minimum elongation (10% vs 12%). Fe550 can reduce the steel area if the structure is designed for it; Fe500 is more ductile.
Which TMT bar is best for house construction?
Fe500 or Fe500D for most houses, and Fe500D in seismic zones. Always follow the grade on your structural drawing.
What does D mean in Fe500D?
D stands for ductile. Fe500D has the same minimum yield strength as Fe500 but higher elongation and tighter limits on carbon, sulphur and phosphorus, so it bends more before breaking.
Can I use Fe550 instead of Fe500?
Using Fe550 bars of the same size and number as an Fe500 design is not weaker, but it saves nothing, and laps may need to be longer. Reducing the bars needs a redesign by the engineer.
How do I calculate the weight of a TMT bar?
Weight in kg per metre is about d² ÷ 162, where d is the diameter in mm. A 12 mm bar weighs about 0.889 kg per metre.
Related guides: RCC full form · M20 vs M25 concrete · One way vs two way slab · Steel weight calculator · All construction guides
Disclaimer: Educational only. Steel grade, bar sizes, laps and detailing must follow your structural drawings, IS 456, IS 13920 and IS 1786, as specified by a qualified engineer. Disclaimer
Tanmay Arora, is an Architect with an experience of 13+ years. He is a Management Grad with a post Graduate Diploma in Building Construction and Materials. Tanmay has worked with renowned firms. He has graduated in Bachelor of Architecture. His deep interest in Architecture and Civil Engineering and his experience has made him one of the best architects a client can think of.
