Hong Life CalculatorsUnderstanding the rebar size chart — concept and principle
This chart shows the nominal diameter, cross-sectional area and weight per metre of Korean deformed reinforcing bars from D10 to D32, together with the closest US bar number. Use it to estimate rebar quantities and weights for an order or a quote, to read structural drawings, or to translate between Korean (KS) and American (ASTM) bar designations.
How it is calculated
The values come from a table, and they follow two simple formulas:
Area A = π × d² ÷ 4 (mm²)
Unit weight = A × 7,850 kg/m³ ÷ 10⁶ ≈ 0.006165 × d² (kg/m)
- d is the nominal diameter in mm, the diameter of a plain round bar with the same mass per metre.
- 7,850 kg/m³ is the standard density of steel.
- The "D" number is the rounded nominal diameter: D16 has d = 15.9 mm.
The principle
Deformed bars have ribs, so their real outline is not a simple circle. Standards therefore define a nominal diameter: the diameter of a smooth bar that would weigh the same per metre. Area and weight are then calculated from that circle. From D10 to D25 the Korean nominal diameters match inch-based ASTM bars #3 to #8; larger sizes are close but not identical (US #10 is 32.3 mm, D32 is 31.8 mm). For US bars #3 to #8 the number is the diameter in eighths of an inch, so #5 = 5/8 inch = 15.875 mm, the same bar as D16.
Worked example
Default input: D16.
- Nominal diameter d = 15.9 mm.
- Area = π × 15.9² ÷ 4 = 198.56 ≈ 198.6 mm².
- Unit weight = 198.56 mm² × 7,850 kg/m³ ÷ 10⁶ = 1.5587 ≈ 1.56 kg/m.
- Closest US size: #5.
An 8 m length of D16 therefore weighs about 1.56 × 8 = 12.5 kg.
How to read the result
Rebar is usually ordered and priced by weight, so total weight = unit weight × total length (including laps, hooks and waste). One tonne of D16 is about 641 m of bar. Area is what engineers use for strength: the tensile capacity of a bar is roughly area × yield strength. The grade, such as SD400 (yield strength 400 MPa), is separate from the size and is marked on the bar.
Common mistakes
- Using the D number itself as the diameter in calculations; use the nominal diameter.
- Forgetting lap lengths, hooks and cutting waste when estimating weight.
- Measuring over the ribs with calipers, which gives a larger number than the nominal diameter.
- Assuming the same size means the same grade or strength.
Frequently asked questions
How much does D13 rebar weigh per metre?
0.995 kg/m.
What is the diameter of D10?
9.53 mm nominal.
Is D16 the same as US #5?
Yes, they share the same nominal diameter (about 15.9 mm), though grades and markings follow different standards.
How do I estimate weight without the table?
Use d² ÷ 162.2 kg/m with d in mm; for D16, 15.9² ÷ 162.2 ≈ 1.56 kg/m.
Sources: KS D 3504, Steel bars for concrete reinforcement · ASTM A615/A615M, Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement