The metal weight formula in Excel starts with one simple relationship: weight equals volume multiplied by density, where volume is the cross-section area of the profile times its length. To turn that into a working spreadsheet, you set up four cells — diameter (or other shape dimension), length, the cross-section formula, and the metal's density — and multiply them together. The result for a 20 mm steel round bar 1000 mm long is about 2.47 kg, a figure that matches the standard steel round bar tables and gives you a known anchor before you start customising the spreadsheet for your own stock. The trick to keeping the formula correct across shapes and units is to convert every input to a single system — typically metres and kilograms per cubic metre — before the multiplication happens. Get that conversion discipline right once, and the same template handles round bar, hex bar, pipe, and sheet without rebuilding from scratch.
The Metal Weight Formula Behind Every Calculation
Every metal weight calculation — whether you do it in Excel, in a dedicated calculator, or on paper — comes back to the same physics equation: weight equals volume multiplied by density. Volume, in turn, equals the cross-section area of the profile multiplied by its length. So the full chain is:
Weight = Cross-section Area × Length × Density
Everything else in this article is just unpacking those three inputs for different shapes and different metals.
Cross-section area depends on the profile shape — a round bar, a square bar, a pipe wall, a flat sheet, and a hex bar all have different geometric expressions. Length is whatever piece you are measuring or quoting. Density is a property of the metal itself, listed in kilograms per cubic metre or pounds per cubic foot. Once you have all three numbers, the multiplication is the easy part. The challenge for most people is keeping units consistent and not mixing millimetres with metres, or inches with feet, halfway through the math. That is also why a structured tool that handles unit conversion internally is useful — but the formulas are the same either way.
Cross-Section Area for Bar, Pipe, Sheet, and Hex
Before any formula goes into an Excel cell, you need the right cross-section expression for the profile in front of you. The five shapes most people need to weigh are covered by the table below.
| Profile | Inputs needed | Cross-section area |
|---|---|---|
| Round bar | Diameter (D), Length (L) | A = π·(D/2)² |
| Square bar | Side (s), Length (L) | A = s² |
| Round tube / pipe | Outer diameter (OD), Wall thickness (t), Length (L) | A = π·((OD/2)² − (OD/2 − t)²) |
| Rectangular sheet / plate | Length, Width, Thickness | A = Length × Width × Thickness (whole volume) |
| Hexagon bar | Across-flats (F), Length (L) | A = (√3/2)·F² |
Two practical points. For round pipe, the formula is the outer disk minus the inner bore — a ring — which is why wall thickness matters and why a solid bar formula will overestimate the weight. For hex bar, the input F is the distance across flats (the wrench size), not the corner-to-corner measurement. Hex stock is sold by A/F, so entering the side length instead will underestimate the bar by a noticeable amount — a 24 mm across-flats hex has roughly 499 mm² of area, while the same side length entered as F gives a smaller, wrong answer.
Building the Calculation in Excel Step by Step
Putting the formula into a spreadsheet is straightforward once the shape is picked. The example below uses a steel round bar 20 mm in diameter and 1000 mm long, the kind of off-the-shelf stock you will find at any metal supplier. Following the steps in order will produce the same 2.47 kg figure that appears in published steel round bar tables, which is a clean sanity check before you trust the template on more unusual sizes.
- Set up the input cells. In A1 enter Diameter (mm), in B1 enter 20. In A2 enter Length (mm), in B2 enter 1000. In A3 enter Density (kg/m³), in B3 enter 7850 (steel).
- Compute the cross-section area in square metres. In B4 enter =(PI()/4)*((B1/1000)^2). PI() returns π, dividing the diameter by 2 and squaring gives r², and π·r² is the circle area. Dividing by 1000 twice converts 20 mm to 0.02 m before squaring, so the answer comes out in m². For a 20 mm bar that is 0.000314 m².
- Compute the volume in cubic metres. In B5 enter =B4*(B2/1000). Multiplying area by length (converted from mm to m) gives the volume of the bar. For a 1000 mm length, the volume is 0.000314 m³.
- Compute the weight in kilograms. In B6 enter =B5*B3. The weight comes out as 0.000314 × 7850 = 2.47 kg, matching what standard steel round bar tables list for a 20 × 1000 mm piece.
- Reuse the formula across rows. Drag the formula down next to every bar in your cutting list. Swap PI() for SQRT(3)/2 if you are working with hex stock, swap the diameter cell for an outer-diameter and wall-thickness pair for pipe, and the same skeleton covers the whole shop.
For a round pipe, the formula becomes =(PI()/4)*((OD/1000)^2 − ((OD/1000) − (wall/1000))^2)*((length)/1000)*density — five terms, same logic. For a rectangular plate it collapses to =length*width*thickness*density because the cross-section area and length are already merged into the volume. Once you have built the template once, you can save it as a master file and copy it for every cutting list that comes through the shop.
The reason most homemade metal weight spreadsheets go wrong is not the formula — it is the units. Mix inches and millimetres and you will be off by a factor of 25. Mix g/cm³ with a length in mm and you will be off by another factor of 1000. A reliable pattern is to convert every input to SI (metres and kilograms per cubic metre) inside the formula, exactly as in step 2 above, and never let raw imperial or metric inputs flow straight into the multiplication. For imperial users, the template is almost identical: keep diameter and length in inches in B1 and B2, switch density in B3 to lb/in³ (steel ≈ 0.284), drop the /1000 conversions, and the multiplication returns pounds directly.
When the Online Calculator Saves You Time
Excel is the right tool when you have a long cutting list, need a price-per-piece column, or want to keep a permanent record of stock weights by part number. For a one-off weight check — a single bar, a single pipe, a single plate — building the spreadsheet from scratch is overkill. The Metal Weight Calculator applies the same five formulas shown above automatically. Pick the profile (round bar, square bar, round tube/pipe, rectangular sheet, or hex bar), pick the metal, and enter the dimensions the shape asks for. The tool returns the weight, plus the cross-section area, the volume, and the density it used, so you can sanity-check the math against your spreadsheet at any time.
Two practical reasons fabricators use a dedicated calculator alongside Excel. It covers all five profile shapes and six common metals in one place, so a hex bar in the middle of a rush job does not need a fresh formula hunt. It also runs entirely in the browser, so there is no Excel file to email, no formulas to retype, and no chance of accidentally editing a constant in cell B3 and silently breaking every downstream row. For shipping and quoting, copy the calculated weight out of the tool directly into a packing list. For a permanent shop record, paste it next to a part number so you have a weight-per-piece lookup without rebuilding the calculation every time someone asks how much the 50 mm hex stock weighs per metre.
Material Densities Used in the Math
The numbers below are the typical engineering values that go into a spreadsheet's density cell. Real alloy density varies a percent or two with grade and temper, so treat these as reference figures and use a mill certificate when you need exact figures.
| Metal | Density (kg/m³) | Notes |
|---|---|---|
| Steel | 7,850 | Generic carbon steel — the default for most shop work |
| Stainless steel (304) | 8,000 | Slightly higher than carbon steel |
| Aluminum | 2,700 | About a third the weight of steel |
| Copper | 8,960 | Heavier than steel, common in electrical work |
| Brass | 8,500 | Copper-zinc alloy |
| Titanium | 4,500 | Strong, light, expensive |
Plugging these into the same 20 × 1000 mm round bar formula shows the spread clearly. Aluminum lands near 0.85 kg, brass near 2.67 kg, titanium near 1.41 kg, and stainless near 2.51 kg for the exact same piece of stock. Run the figure for your own alloy before you quote or place a freight booking, especially for heavier metals where a small density error scales into a real kilogram count on a pallet of pipe.
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