Material Weight and Cost Calculator

What this tool does

CM8-01 calculates the theoretical weight and material cost of metal and plastic stock from its profile and dimensions. It covers 12 common profiles — bar, sheet/plate, tube and structural sections — and library materials, plus custom density entry. Supplier pricing is entered manually. Build multi-line cut lists, edit or duplicate lines, export CSV for your ERP or quote, and save complete projects as local JSON files.

Everything runs inside this single HTML file. No installation, no account, no network requests — your dimensions, prices and cut lists never leave your computer.

Fundamentals

Weight comes from density

Every calculation in this tool reduces to one physical relationship:

Density (ρ) is mass per unit volume, expressed here as kg/m³ (metric) or lb/in³ (imperial). Mild steel is about 7,850 kg/m³ — meaning a solid cube of steel one metre on each side weighs 7.85 tonnes. Aluminum, at ~2,700 kg/m³, is roughly one-third that: this is why identical parts in aluminum weigh about 35% of their steel equivalents.

Linear stock: area × length

Bars, tubes and structural sections have a constant cross-section, so their volume is simply the cross-section area multiplied by the length:

This is also why suppliers publish weight per metre (kg/m) or weight per foot (lb/ft): it's just A × ρ, a property of the profile alone. The tool shows this linear weight for every linear profile — handy for checking a supplier's catalogue numbers or estimating from stock lengths.

Internal units

The tool computes in millimetres and kilograms internally and converts at the boundary: 1 in = 25.4 mm (exact), 1 kg = 2.204623 lb, 1 lb/in³ = 27,679.9 kg/m³. Switching units converts your current inputs automatically — no re-typing.

Shape formulas

Cross-section area formulas used for each profile. Structural sections (angle, channel, I-beam, tee) use the standard sharp-corner approximation — real rolled sections have fillet radii and slight taper, so catalogue weights can differ by a few percent (see Accuracy).

• Profile — Formula — Variables

Density reference

Library values are standard handbook densities for the most common temper/condition of each grade. Alloy chemistry varies slightly between producers; if your material certificate lists a density, use it — the density field is always editable.

• Material — kg/m³ — lb/in³

Pricing guidance

The calculator intentionally does not load a market price. Enter the price from your supplier quotation, purchase order, contract or approved internal material table. Material prices vary substantially by alloy, form, size, quantity, certification, processing, freight and location.

• Match the quoted unit: enter price per kilogram in metric mode or per pound in imperial mode. Switching units converts the entered price correctly while preserving its internal per-kilogram value.
• Use the correct product form: sheet, plate, bar and tube can have different prices even for the same alloy and specification.
• Include applicable extras: alloy surcharge, cut charge, certification, testing, freight, minimum-order charges and taxes may be separate from the base material price.
• Verify before purchase: calculated cost is an estimate based on the price and allowance you enter.

Buying allowances: scrap, kerf and drop

You almost never buy exactly the finished weight. The scrap / kerf allowance field adds a percentage on top of the net weight to reflect what you actually purchase:

• Kerf — material destroyed by the cut itself. A cold saw or bandsaw removes 2–3 mm per cut; plasma and oxy-fuel more; laser and waterjet less (0.1–1 mm). Many small parts from one bar means many kerfs.
• Drop / remnant — the unusable end of a stock length. Cutting 900 mm parts from a 6 m bar leaves a 600 mm drop after six parts (plus kerf), i.e. ~10% of the bar.
• Facing and cleanup stock — machining allowance on each end, skin cuts on plate.
• Nesting yield — on sheet and plate, the ratio of part area to sheet area. 70–85% yield is common for irregular profiles; the remainder is your allowance.

Typical planning values: 3–5% for simple saw-cut bar work, 8–15% for multi-part bar jobs with drops, 15–30% for nested sheet/plate parts. Standard stock lengths to plan around: bar and tube commonly come in 3 m, 6 m (20 ft), and 12 ft lengths; sheet in 4×8 ft (1220×2440 mm) and 5×10 ft (1524×3048 mm).

Accuracy: theoretical vs. actual weight

This tool computes theoretical weight from nominal dimensions. Real material differs:

• Mill tolerance: plate is rolled to a thickness tolerance that is usually plus-biased — actual plate often weighs 2–5% more than theoretical. Trade practice for structural sections allows roughly ±2.5% on weight.
• Sharp-corner approximation: the angle/channel/beam formulas here ignore fillet radii and flange taper. Against published catalogue weights (e.g. CISC / AISC section tables) expect small differences — use catalogue values for certified structural take-offs.
• Pipe vs. tube: pipe is specified by nominal pipe size (NPS) and schedule, not by its true OD. Use the actual OD and wall from a pipe chart (e.g. NPS 1½ Sch 40 = 48.3 mm OD × 3.68 mm wall) in the round-tube profile.
• Coatings: galvanizing adds roughly 3–6% to steel weight depending on coating class.

For estimating, quoting and shipping-weight purposes, theoretical weight with a sensible allowance is standard practice. For legal-for-trade or certified lifting weights, weigh the material.

Unit conversions used

• Convert — Multiply by
• inches → millimetres — 25.4 (exact)
• kilograms → pounds — 2.2046226
• kg/m → lb/ft — 0.6719690
• kg/m³ → lb/in³ — 0.0000361273
• metres → feet — 3.2808399
• mm² → in² — 0.0015500
• price per kg → price per lb — 0.4535924

Saving your work

• Autosave: your unit choice, currency and cut list are kept in this browser's local storage automatically (when the browser allows it) and restored next time you open the file.
• Save project (.json): saves the complete calculator state and cut list, including profile, dimensions, material, density override, quantity, allowance, price, currency and item notes.
• Export CSV: a spreadsheet-ready cut list for quotes, ERPs and purchase orders.
• Print Report: produces a client-ready report — executive summary tiles, the full bill of materials and the cost & weight charts. Fill in the Report details card (title, company / project, prepared by and closing notes) on the Cut List tab; those fields are saved with the project and printed in the report header and footer. The browser print dialog → “Save as PDF” gives you a shareable document.