Introduction
The Steel Pipe Weight Calculator returns a per-foot weight from just two inputs — outside diameter and wall thickness — using one compact formula: W = 10.68 × (OD − wall) × wall. It looks like a magic constant, but every digit of 10.68 comes from the density of steel and the geometry of a hollow cylinder. This guide derives the formula from first principles, verifies it against published ASME weights, explains the metric version, and shows exactly when to trust the formula versus a printed table.
The Imperial Formula
W (lb/ft) = 10.68 × (OD − wall) × wall, where OD and wall thickness are both in inches.
That’s the entire calculation. Enter OD = 4.500 in and wall = 0.237 in (4-in Sch 40), and you get 10.68 × 4.263 × 0.237 = 10.79 lb/ft — the published ASME B36.10M value. The formula applies to any round steel pipe: Sch 40, Sch 80, XS, XXS, or a non-standard wall you measured with calipers. It also works for tubing generally, since the derivation assumes nothing pipe-specific beyond a circular cross-section.
Where Does 10.68 Come From?
The constant is density times geometry, with unit conversions folded in. Here’s the derivation:
Step 1 — Cross-sectional area of the steel. A pipe is an annulus: outer circle minus inner circle. With OD as outside diameter and wall as wall thickness, the inside diameter is (OD − 2 × wall), so:
Area = π/4 × [OD² − (OD − 2 × wall)²] = π × (OD − wall) × wall (square inches).
Step 2 — Weight per foot. Multiply the area (in²) by 12 inches of length to get cubic inches per foot of pipe, then by the density of carbon steel, 0.2836 lb/in³ (which is 490 lb/ft³ ÷ 1,728 in³/ft³):
W = π × (OD − wall) × wall × 12 × 0.2836 = π × 12 × 0.2836 × (OD − wall) × wall.
Step 3 — Evaluate the constant. π × 12 × 0.2836 = 10.692… The industry-standard value rounds this to 10.68, a slightly conservative figure baked into ASME B36.10M. So:
W = 10.68 × (OD − wall) × wall
No π, no density lookup, no unit juggling — all of it is pre-computed into 10.68. The only requirement is that OD and wall share the same units (inches), and the answer comes out in lb/ft.
The Metric Formula
W (kg/m) = 0.0246615 × (OD − wall) × wall, with OD and wall in millimeters.
The derivation is identical, starting from steel density 7,850 kg/m³. Working through the same annulus geometry with millimeters and meters: constant = π × 7,850 ÷ 1,000,000 = 0.0246615. The two formulas are the same physics in different units — they must agree, and they do. Take 4-in Sch 40 (OD 114.3 mm, wall 6.02 mm): 0.0246615 × (114.3 − 6.02) × 6.02 = 0.0246615 × 108.28 × 6.02 = 16.08 kg/m, versus 10.79 lb/ft × 1.48816 = 16.06 kg/m. The 0.1% difference is rounding in the published per-foot value, not an error — both are correct to the precision of the inputs.
Practical note: 1 lb/ft = 1.48816 kg/m, and 1 kg/m = 0.67197 lb/ft. These are exact conversion factors, so converting a result between unit systems never introduces formula error — any mismatch you see comes from rounded inputs.
Verification Against Published Tables
A formula is only as good as its agreement with reality. Here the imperial formula is checked against published ASME B36.10M Sch 40 weights across the full size range, using standard OD and wall values:
| NPS (in) | OD (in) | Wall (in) | Formula (lb/ft) | Published (lb/ft) |
|---|---|---|---|---|
| 1/2 | 0.840 | 0.109 | 0.851 | 0.85 |
| 3/4 | 1.050 | 0.113 | 1.131 | 1.13 |
| 1 | 1.315 | 0.133 | 1.679 | 1.68 |
| 1-1/2 | 1.900 | 0.145 | 2.718 | 2.72 |
| 2 | 2.375 | 0.154 | 3.653 | 3.65 |
| 3 | 3.500 | 0.216 | 7.576 | 7.58 |
| 4 | 4.500 | 0.237 | 10.790 | 10.79 |
| 6 | 6.625 | 0.280 | 18.974 | 18.97 |
| 8 | 8.625 | 0.322 | 28.554 | 28.55 |
| 10 | 10.75 | 0.365 | 40.483 | 40.48 |
| 12 | 12.75 | 0.375 | 49.562 | 49.56 |
Every size agrees within 0.005 lb/ft — the residual is rounding in the published two-decimal values, since the tables themselves were generated from this same formula. This is why the calculator can accept a measured wall thickness from calipers and still return a trustworthy number: the formula is the table.
For the terminology behind these inputs — NPS, OD, and schedule — see the complete guide; the most common input errors are catalogued in the common mistakes guide.
Worked Examples
Example 1: A 21-ft stick of 2-in Sch 40
OD = 2.375 in, wall = 0.154 in. W = 10.68 × (2.375 − 0.154) × 0.154 = 10.68 × 2.221 × 0.154 = 3.65 lb/ft. Total: 21 × 3.65 = 76.65 lb, or 76.65 × 0.453592 = 34.8 kg.
Metric check: 21 ft = 6.4008 m; 3.65 × 1.48816 = 5.432 kg/m; 6.4008 × 5.432 = 34.8 kg. Identical.
Example 2: Sch 40 vs Sch 80 on 4-inch pipe
Same OD (4.500 in), different walls. Sch 40 (0.237 in): 10.68 × 4.263 × 0.237 = 10.79 lb/ft. Sch 80 (0.337 in): 10.68 × 4.163 × 0.337 = 14.98 lb/ft. The ratio 14.98 ÷ 10.79 = 1.388 — Sch 80 is ~39% heavier, a difference the formula captures exactly because the OD term is unchanged and only the wall terms move.
Example 3: A non-standard measured wall
Calipers read 0.200 in wall on a 3.500-in OD pipe (between Sch 40’s 0.216 and lighter walls — possibly corroded or a mill-light lot). W = 10.68 × (3.500 − 0.200) × 0.200 = 10.68 × 3.300 × 0.200 = 7.05 lb/ft. No table lists this pipe; the formula handles it anyway.
Formula vs. Table: When to Use Which
- Use the formula when you have measured dimensions (calipers, ultrasonic gauge), non-standard walls, or you’re working in metric and want kg/m directly.
- Use published tables for quick lookups of standard sizes, or when documentation needs to cite an ASME reference value.
- Cross-check one against the other whenever the number matters — a truck load, a support design, a per-ton quote. If formula and table disagree by more than rounding, one of your inputs is wrong (usually NPS entered as OD).
Remember the formula’s limits: it computes the theoretical weight of plain-end bare pipe at nominal dimensions. Mill wall tolerance (±12.5% is typical), coatings, and attached fittings all shift real weight away from the theoretical value. Material grades change the answer only slightly — A53, A106, and API 5L are all carbon steels with effectively the same density; grade affects strength and certification, not weight, as explained in the material guide. And the formula says nothing about pressure capacity — that analysis belongs to the applicable piping code and a licensed engineer.
Related Guides
- Steel Pipe Weight Calculator: Complete Guide — terminology, tables, and a full worked example.
- FAQ — quick answers to the most asked questions.
- Material Guide — grades, schedules, and coatings explained.
- Estimating Guide — from takeoff to a complete project weight estimate.
- Pre-Order Checklist — everything to verify before you buy pipe.
Get Your Number
The 10.68 constant is just density times geometry, pre-computed: it reproduces every published ASME weight within rounding and handles any wall you can measure. The Steel Pipe Weight Calculator runs this formula in both unit systems — enter OD and wall, get per-foot and total weight instantly, and cross-check the result against the table above whenever the load matters.
Disclaimer: Calculator results are planning estimates based on the dimensions you enter. Actual pipe weight varies with mill tolerances, coatings, and fittings. This tool does not determine pressure ratings or structural adequacy. Verify weights with your supplier and consult a licensed professional or your local building authority for pressure, structural, or code-related decisions.
