Introduction
US construction materials arrive with imperial DNA: steel sections rated in lb/ft, rebar with imperial size numbers, fasteners sold by the pound, cement in 80-lb bags. When the crew, the fab shop, or the freight paperwork works in metric, converting product tables correctly is a skilled task — and product tables are where the per-length and density conversions that trip people up live.
The Pounds to KG Calculator handles the straight mass conversions on this page. This guide covers the rest: how each material category is labeled, how to convert its tables systematically, the density table in both unit systems, and where to cross-check against dedicated weight calculators.
Structural Steel: lb/ft Is the Native Language
Wide-flange beams are designated by depth and weight per foot — a W12x26 is nominally 12 inches deep and weighs 26 lb per foot. Plates, channels, angles, and hollow sections follow the same convention. Converting a steel schedule means converting two things: the member weight (lb → kg) and the unit length (per foot → per meter).
The combined factor: 1 lb/ft = 1.48816 kg/m. So the W12x26 runs at 26 × 1.48816 = 38.69 kg/m, and a 20-ft piece weighs 520 lb = 235.87 kg (check it both ways: 38.6923 kg/m × 6.096 m = 235.87 kg — the two paths agree, which is how you know the conversion is sound).
Worked example: a small schedule of six W12x26 pieces at 20 ft each. Native total: 6 × 20 × 26 = 3,120 lb. Convert once: 3,120 × 0.45359237 = 1,415.21 kg (≈1.415 tonnes). For full beam-by-beam weight takeoffs with section properties, the steel beam weight calculator is the dedicated tool — use it for the native-unit takeoff, then convert the summary total with the method on this page.
Rebar: Imperial Sizes, Metric Jobsites
US rebar sizes (#3 through #18) are numbered in eighths of an inch of diameter, and bar weights are published in lb per linear foot: #4 is 0.668 lb/ft, #5 is 1.043 lb/ft, #6 is 1.502 lb/ft, #9 is 3.400 lb/ft. On metric jobsites these become kg/m via the same 1.48816 factor:
| Bar size | Weight (lb/ft) | Weight (kg/m) |
|---|---|---|
| #4 | 0.668 | 0.994 |
| #5 | 1.043 | 1.552 |
| #6 | 1.502 | 2.235 |
| #8 | 2.670 | 3.973 |
| #9 | 3.400 | 5.060 |
| #11 | 5.313 | 7.907 |
Check one: 0.668 × 1.48816 = 0.99409 → 0.994 ✓. Rebar is also bundled by weight — a typical bundle runs 1,500–2,500 lb (680–1,134 kg) — so bundle counts on a metric packing list need the straight mass conversion. For bar counts, laps, and total weights from a bending schedule, the rebar weight calculator does the native-unit takeoff; convert its total with the method on this page rather than converting bar by bar. The estimating guide walks through that exact workflow.
Fasteners: Sold by the Pound, Counted by the Thousand
Bolts, nuts, screws, and nails are sold by weight — per pound, per 100-lb keg, or per hundredweight — while the job needs a count. The conversion chain for a metric order:
- Count needed → weight in lb (from the supplier’s pieces-per-pound figure).
- Weight in lb → weight in kg (× 0.45359237).
Example: 2,000 structural bolts at 42 pieces per pound = 47.62 lb → 21.60 kg. Order the count, but ship and receive against the kg weight — freight and customs care about kilograms, the crew cares about pieces, and the conversion connects them. Keep the pieces-per-pound figure with the order; it’s the one number that can’t be reconstructed from the weight alone.
Bagged Goods: The 50-lb and 80-lb Standards
Cement, mortar mix, grout, and anchoring cement are commonly packed in 50-lb (22.68 kg) and 80-lb (36.29 kg) bags — check: 80 × 0.45359237 = 36.287 → 36.29 kg. Bag counts convert through the lot total: 120 eighty-pound bags = 9,600 lb = 4,354.49 kg (≈4.35 tonnes). Pallet quantities follow the same path — a 40-bag pallet of 80-lb bags is 3,200 lb = 1,451.50 kg.
The practical trap: mixed bag sizes on one pallet or one order. Convert each size’s subtotal separately, then add the kilogram subtotals — this is the one case where converting subtotals (not individual bags) is the right granularity, because the bag is the indivisible unit the supplier ships.
Density Table: Both Unit Systems
When you need weight from volume — a concrete pour, a steel plate, water in a tank — density does the work, and it must be in the unit system you’re computing in:
| Material | Density (lb/ft³) | Density (kg/m³) |
|---|---|---|
| Structural steel | 490 | 7,849 |
| Normal-weight concrete | 150 | 2,403 |
| Water | 62.4 | 1,000 |
| Gravel / crushed stone | 95–110 | 1,522–1,762 |
| Sand, dry | 90–110 | 1,442–1,762 |
| Douglas fir, structural | 32–36 | 513–577 |
Conversion factor for densities: 1 lb/ft³ = 16.0185 kg/m³. Verify a row: 490 × 16.0185 = 7,849.07 → 7,849 ✓. Aggregates and lumber vary with moisture and species — treat the ranges as planning values and the steel/concrete/water rows as constants.
Worked density example: a concrete footing 10 ft × 10 ft × 1 ft = 100 ft³. At 150 lb/ft³ that’s 15,000 lb; at 2,403 kg/m³ over 2.8317 m³ that’s 6,804.5 kg — and 15,000 × 0.45359237 = 6,803.89 kg. The two paths agree within rounding, which is the check that both densities were applied correctly. (The small gap is the rounded 2,403 vs the exact 2,402.77 — carry the unrounded density for final numbers.)
Converting a Full Product Table: Method
When a supplier sends a ten-page table in imperial and the job needs metric:
- Identify every unit in the table — lb, lb/ft, lb/ft², $/CWT — before converting anything. Mixed-unit tables are the norm, not the exception.
- Convert the unit columns once (× 1.48816 for lb/ft, × 16.0185 for lb/ft³) and add metric columns beside the imperial ones, rather than replacing them. Two columns, both labeled, beats one converted column that nobody can audit.
- Spot-check with the inverse on two or three rows: convert a kg/m value back and confirm the original lb/ft. The pro tips guide makes this a standing habit.
- Convert order totals from the imperial column, not by summing the metric column — keeps rounding in one place. The one exception is bagged goods at mixed sizes, noted above.
For the theory behind each factor, the formula-explained guide derives them all; for the failure modes, the common mistakes guide shows what skipping each step costs.
Related Guides
- Complete Guide — the full overview of lb-to-kg conversion in construction.
- Estimating Guide — take off in native units, convert the summary.
- Formula Explained — the density and per-length factors derived.
- Case Study — a hypothetical steel schedule converted for a metric fab shop.
- FAQ — quick answers to the most asked conversion questions.
- Conversion Checklist — pre-order and pre-lift verification steps.
Frequently Asked Questions
What is 1 lb/ft in kg/m?
1.48816 kg/m. A 26 lb/ft steel section is 38.69 kg/m.
What is the density of steel in kg/m³?
7,849 kg/m³ (from 490 lb/ft³). Concrete is 2,403 kg/m³; water is 1,000 kg/m³.
How heavy is an 80-lb bag of cement in kg?
36.29 kg. A 50-lb bag is 22.68 kg.
Should I convert a product table row by row?
Add converted columns beside the imperial ones for reference, but compute order totals from the imperial column and convert the total — one rounding point instead of dozens.
Get Your Number
Material conversion is table work, not guesswork: identify every unit in the table, apply the right factor to each (1.48816 for lb/ft, 16.0185 for lb/ft³, 0.45359237 for plain lb), keep both columns labeled, and convert totals from the native-unit column. Do the native-unit takeoff in the steel or rebar calculator, then bring the total to the Pounds to KG Calculator for the final conversion — and spot-check the round trip before it becomes an order.
Disclaimer: Pound-to-kilogram conversions are exact mathematics, but results are only as good as the values entered — always verify weights with your supplier or equipment data plate before ordering or lifting, and consult a licensed professional or your local building authority for structural or code-related decisions.
