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Calculate rebar quantity, length, and weight for Japan JIS D10-D22 deformed bars. Single or double layer supported.

📘 How to Use

  1. Enter the slab width and length in millimeters as shown on the Japan-side drawings (the calculator follows JIS metric conventions).
  2. Select the JIS bar designation (D10 to D22) and choose single-layer or double-layer (top plus bottom) reinforcement.
  3. Adjust the spacing slider between 100 mm and 300 mm to match the pitch called out in the rebar schedule.
  4. Read off the bar counts per direction, the total length in meters, and the theoretical weight in kilograms.

JIS Rebar Spacing Calculator (Japan D10-D22)

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Total bars —
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Estimated weight —

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Article

JIS Rebar Calculator (D10-D22) | A Reference for Engineers Working Japan Projects

If your firm has just been pulled into a Japan-based project—a factory build-out, an automotive plant retrofit, a JV with a Japanese GC—the rebar schedule will arrive in JIS designations (D10, D13, D16, D19, D22) rather than the ASTM bar numbers you are used to. This calculator runs the bar-count, total length, and steel weight math directly in JIS units and unit weights, so estimators and project engineers can verify quantities without translating each line of a Japanese drawing into US imperial sizes first.

💡 About this tool

  • Direct JIS Input, No Conversion Step Slab dimensions are entered in millimeters and bar sizes are picked from the five JIS standard deformed bars (D10 through D22). The unit weight for each diameter is the official JIS G 3112 value—0.560 kg/m for D10 up to 3.04 kg/m for D22—so the kilograms you read off can be cross-checked against the mill certificate without arithmetic.
  • Real-Time Layout Diagram As you change the spacing slider or layer count, the canvas redraws the bar pattern on the slab. This is handy when reviewing a Japan-side drawing: dial in the schedule, glance at the diagram, and confirm whether the GC's pitch matches the structural sheet.
  • No Take-Off Adjustment The weight returned is the theoretical net weight along the clear slab dimensions. Lap splice length, anchorage hooks, and cutting waste are not included; standard procurement allowance in Japan ranges from 5% to 15% on top of this figure depending on the supplier and the splice density.

🧐 Frequently Asked Questions

Q. How does a JIS D-size map to a US ASTM bar number?

A. D-sizes name the nominal diameter in millimeters; ASTM bar numbers are eighths of an inch. The everyday cross-reference looks like this: D10 ≈ #3 (9.53 mm vs 9.5 mm nominal), D13 ≈ #4 (12.7 mm in both), D16 ≈ #5 (15.9 mm in both), D19 ≈ #6 (19.1 mm in both), D22 ≈ #7 (22.2 mm in both). The diameters are close but the unit weights and rib geometries are defined under different standards, so the equivalence is for orientation only — the actual specified bar on a Japan-side drawing is the JIS bar.

Q. The drawing notes call out SD295 or SD345 grade. Does this calculator care?

A. No. The geometry (counts, length) and the unit weight (kg/m) are diameter-driven and the same across SD295A, SD295B, SD345, SD390, and SD490. Grade only affects yield strength and elongation, which matter for the structural design but not for material take-off. Pick the diameter from the drawing and the calculator's output is correct regardless of grade.

Q. Can we use this output directly for procurement from a Japanese supplier?

A. Treat it as the engineering take-off baseline. Japanese fabricators expect a list called a haikin-list (配筋リスト) with per-bar lengths after cut-and-bend, lap allowance, and bender turn-up. Most distributors quote in metric tons and add their own 5–15% loss factor on top of the geometric figure shown here.

📚 Why Japanese Drawings Use the D Prefix

Japan adopted the metric deformed-bar designation in JIS G 3112, naming each size by its approximate nominal diameter in millimeters. The "D" stands for deformed, distinguishing modern ribbed rebar from the plain round bar (often labeled with the "φ" prefix) that older Japanese specifications and some non-structural applications still call out. Once the diameter is named, the JIS standard fixes the nominal cross-section, the unit weight, and the rib geometry, so any D13 from any JIS-certified mill in Japan is metrologically interchangeable. This is why Japanese rebar schedules look terse: the diameter call-out is sufficient, the rest is locked by the standard. The downside for foreign teams is that the imperial-trained eye has to do a one-time mental conversion (D13 = 12.7 mm ≈ #4), but once converted the math is identical to what an ASTM #4 reader does in their own market.