You've probably typed "how many kg in a meter" into Google at 2 AM while staring at a steel beam spec sheet, a fabric roll, or a shipping manifest. Maybe you're pricing rebar. Day to day, maybe you're sewing a weighted blanket. Maybe you're just trying to win an argument with your brother-in-law.
Here's the short answer: none.
Kilograms measure mass. Think about it: asking how many kilograms in a meter is like asking how many gallons in an hour. Worth adding: meters measure length. The units don't talk to each other — not directly.
But you didn't come here for a physics lecture. You came here because you have a thing* that's measured in meters, and you need to know what it weighs. Or you have a weight limit in kilograms, and you need to know how much length that buys you.
Let's fix the question.
What You're Actually Looking For: Linear Density
The real concept hiding behind your search is linear density — mass per unit length. The unit you want is kilograms per meter (kg/m).
This shows up everywhere:
- Steel rebar: 0.But 888 kg/m for 12mm, 1. 579 kg/m for 16mm
- Copper wire: varies by gauge, but 2.5mm² is roughly 0.
If you know the kg/m of a material, you can calculate weight from length. Or length from weight. That's the conversion you actually need.
The formula is stupidly simple
Weight (kg) = Length (m) × Linear Density (kg/m)
Length (m) = Weight (kg) ÷ Linear Density (kg/m)
That's it. The hard part isn't the math. It's finding the right linear density number for your* specific material, in your* specific condition.
Why This Trips People Up
Most people don't realize that "kg per meter" isn't a universal constant for a material. It changes with:
Cross-sectional area — A 20mm steel bar weighs 2.47 kg/m. A 10mm bar of the same steel* weighs 0.617 kg/m. Same material, four times the weight per meter.
Alloy/composition — 6061-T6 aluminum weighs 2.70 g/cm³. 7075-T6 weighs 2.81 g/cm³. That 4% difference adds up fast on a 6-meter extrusion run.
Hollow vs. solid — 50mm OD steel tube with 3mm wall: ~3.5 kg/m. Same OD, 5mm wall: ~5.7 kg/m. Solid 50mm bar: ~15.4 kg/m.
Moisture content — Wood, fabric, rope, insulation — all absorb water. Kiln-dried pine at 12% MC weighs way less than green pine at 40% MC. Same species, same dimensions, wildly different kg/m.
Temperature — Minor for most stuff, but critical for precision work. A 100m aluminum busbar expands ~2.3mm per 10°C rise. Mass stays same. Linear density drops* because length increases.
I've seen engineers spec "aluminum extrusion, 40x40mm, 2 kg/m" and order 500 meters — only to receive a different alloy profile that runs 2.3 kg/m. That's 150 extra kg on the truck. Shipping cost blew the budget.
Common Materials: Real-World kg/m Reference
Steel (mild, ~7.85 g/cm³)
| Profile | Dimensions | Approx kg/m |
|---|---|---|
| Round bar | 6mm | 0.And 222 |
| Round bar | 10mm | 0. 617 |
| Round bar | 12mm | 0.888 |
| Round bar | 16mm | 1.Worth adding: 579 |
| Round bar | 20mm | 2. 466 |
| Square bar | 25×25mm | 3.85 |
| Flat bar | 50×10mm | 3.93 |
| Angle | 50×50×5mm | 3.That said, 77 |
| Pipe | 50mm NB, Sch 40 | 5. 74 |
| H-beam | 150×75mm (UB) | 14. |
Aluminum (6061-T6, ~2.70 g/cm³)
| Profile | Dimensions | Approx kg/m |
|---|---|---|
| Round bar | 10mm | 0.07 |
| Rect tube | 80×40×4mm | 2.That said, 212 |
| Round bar | 20mm | 0. Practically speaking, 31 |
| Angle | 50×50×5mm | 1. 848 |
| Square tube | 40×40×3mm | 1.30 |
| Channel | 100×50mm | 2. |
Copper (pure, ~8.96 g/cm³)
| Type | Size | Approx kg/m |
|---|---|---|
| Round wire | 2.240 | |
| Busbar | 50×10mm | 4.5mm² (solid) |
| Round wire | 10mm² (stranded) | 0.Worth adding: 060 |
| Round wire | 6mm² (solid) | 0. 48 |
| Pipe | 15mm OD × 1mm wall | 0. |
Stainless Steel (304, ~7.93 g/cm³)
Add ~1% to mild steel weights. Close enough for estimating. For precision, check the mill cert.
Want to learn more? We recommend how many cups are in a pint and how many days is 3 weeks for further reading.
Plastics (varies wildly)
| Material | Density (g/cm³) | 10mm round bar kg/m |
|---|---|---|
| PVC (rigid) | 1.So naturally, 95 | 0. 38 |
| PTFE (Teflon) | 2.18 | 0.173 |
| Acrylic | 1.Think about it: 075 | |
| Nylon 6/6 | 1. 108 | |
| HDPE | 0.14 | 0.Even so, 093 |
| Polycarbonate | 1. 20 | 0.20 |
Wood (air-dried, ~12% MC)
| Species | Density (kg/m³) | 100×50mm (2×4) kg/m |
|---|---|---|
| Pine (radiata) | 480 | 2.4 |
| Douglas fir | 530 | 2.65 |
| Oak (European) | 720 | 3.6 |
| Meranti | 550 | 2. |
Wood (air-dried, ~12% MC)
| Species | Density (kg/m³) | 100×50mm (2×4) kg/m |
|---|---|---|
| Pine (radiata) | 480 | 2.4 |
| Douglas fir | 530 | 2.65 |
| Oak (European) | 720 | 3.Which means 6 |
| Meranti | 550 | 2. 75 |
| Plywood (18mm) | 600 | 3. |
Brass (70/30, ~8.5 g/cm³)
| Profile | Dimensions | Approx kg/m |
|---|---|---|
| Round bar | 10mm | 0.66 |
| Round bar | 20mm | 2.67 |
| Round bar | 25mm | 4.Now, 05 |
| Square bar | 30×30mm | 7. 65 |
| Hex bar | 19mm A/F | 2. |
Bronze (phosphor, ~8.7
| Profile | Dimensions | Approx kg/m |
|---|---|---|
| Round bar | 10mm | 0.68 |
| Round bar | 20mm | 2.Consider this: 73 |
| Round bar | 25mm | 4. 26 |
| Square bar | 30×30mm | 7.83 |
| Bearing strip | 50×10mm | 4. |
Titanium (Grade 5, ~4.43 g/cm³)
| Profile | Dimensions | Approx kg/m |
|---|---|---|
| Round bar | 10mm | 0.Now, 35 |
| Round bar | 25mm | 2. 17 |
| Sheet | 1mm × 1m wide | 4.43 |
| Tube | 50×3mm | 1. |
Quick Mental Math Shortcuts
Steel: kg/m ≈ cross-section (mm²) × 0.00785
Aluminum: kg/m ≈ cross-section (mm²) × 0.0027
Copper/Brass/Bronze: kg/m ≈ cross-section (mm²) × 0.0085–0.009
Plastics: kg/m ≈ cross-section (mm²) × density (g/cm³) × 0.001
Example: 40×40×3mm square tube. On top of that, cross-section = 40² − 34² = 444 mm². Now, steel: 444 × 0. 00785 ≈ 3.Because of that, 49 kg/m. Aluminum: 444 × 0.0027 ≈ 1.20 kg/m.
The "Trust But Verify" Checklist
Before you cut the PO:
- Request the mill certificate — it lists actual density and dimensional tolerances
- Check the standard — EN 10210 vs EN 10219 hollow sections differ in corner radii, changing weight by 2–4%
- Confirm surface condition — hot-rolled scale adds ~1.5%; galvanizing adds 3–6% depending on dip thickness
- Ask for "theoretical" vs "actual" weight — some suppliers invoice on theoretical; others weigh each bundle
- Factor waste — add 3–5% for offcuts, 5–10% for complex fabrication
When Weight Drives Design
Weight isn't just a shipping line item. It dictates:
- Foundation sizing — a 15% weight overrun on a mezzanine means re-pouring footings
- Lifting plan — that "2.2 tonne" beam at 2.5 tonnes exceeds the 2.5t crane capacity once rigging is added
- Seismic mass — in high-seismic zones, every kilogram attracts lateral force
- Transport permits — 40ft container payload ~26.5t; 500m of 2.3 kg/m = 1.15t. Fine. But 500m of 14 kg/m H-beam = 7t. Two containers. Different budget.
Final Word
The kg/m column on a datasheet is a nominal* number. Reality lives in the mill cert, the caliper, and the weighbridge ticket. Treat published weights as the starting assumption — not the final answer. Now, verify before you order. Weigh when it arrives. Design for the actual mass, not the catalog mass.
Your structure doesn't read the brochure. It feels the gravity.
