SizingKitGrade, and how to tell
Stainless steel weight calculator
Weight per foot and per order for stainless bar, plate, tube and angle, with 304, 316 and 410 priced as three grades instead of one average — free and with no signup. The austenitic grades are 8.00 g/cm³ and martensitic 410 is 7.70, a 3.90% gap that a single “stainless” density hides; on a 20,000 lb order it is 750 lb of metal. A magnet settles which family you are holding in about a second, and the page says what it cannot settle.
- 100% free
- No signup
- 3 grades apart
- Magnet test built in
- Order-scale error shown
The stock, and which grade it actually is
Ordered by decimal thickness far more often than by gauge, because the ASTM A480 tolerance band is a real fraction of a thin sheet and the gauge number adds nothing once a decimal is on the purchase order.
Two figures, not three: 304 and 316 are both 8.00 g/cm³ to the precision anybody publishes, and 410 is the one that is different.
The quantity field is what decides whether the grade question is worth asking at all: 3.75% is invisible on one bracket and a pallet on a coil order. Sizes are read in inches and the stock length in feet.
STAINLESS 304 / 304L
PER FOOT
1.7341 lb
2.5806 kg/m
THE WHOLE ORDER
1734.1 lb
786.6 kg · 50 × 34.68 lb
Priced as an austenitic grade this order is 1734.1 lb; priced as 410 it is 1669.1 lb. The 65 lb between them is the cost of treating “stainless” as one density, and it grows with every length you add.
Density 0.28902 lb/in³. AISI 304 austenitic stainless (ASTM A240 UNS S30400): 8.00 g/cm³, the published density for the 18-8 austenitic grades. 7.9–8.0 across the austenitic 300 series. 321 and 347 sit with 304; 316 and 317 run a shade higher for their molybdenum. Cold work raises it a fraction by closing porosity but not measurably.
The magnet test, and exactly how far it gets you
Fair enough — the magnet only ever narrows this to a family anyway, and if the mill certificate is in front of you it has already answered the question the magnet cannot.
The three grades, and carbon steel for scale
The gap that matters is between the families, not within them: 3.9% between austenitic and martensitic, against nothing measurable between 304 and 316.
| Grade | Family | Magnet | g/cm³ | lb/in³ | lb/ft | Order, lb |
|---|---|---|---|---|---|---|
| Stainless 410 (martensitic) | Martensitic | Sticks | 7.70 | 0.27818 | 1.6691 | 1669.1 |
| Stainless 304 / 304L | Austenitic | Falls off when annealed | 8.00 | 0.28902 | 1.7341 | 1734.1 |
| Stainless 316 / 316L | Austenitic | Falls off when annealed | 8.00 | 0.28902 | 1.7341 | 1734.1 |
| Carbon steel | Ferritic / pearlitic | Sticks | 7.85 | 0.2836 | 1.7016 | 1701.6 |
Published nominal densities of the named alloys, from the ASTM and Aluminum Association specifications cited row by row. Stored as g/cm³ × 1000; lb/in³ and lb/ft³ are converted at the exact definitions of the pound and the inch (1 lb/in³ = 27,679.9047 kg/m³), not transcribed separately.
Why the two families weigh differently. AISI 410 martensitic stainless (ASTM A240 UNS S41000): 7.70 g/cm³. The martensitic and ferritic grades are lighter than the austenitic ones because they have no nickel and a different crystal structure. The nickel that makes an austenitic grade austenitic is itself denser than iron, and the face-centered cubic lattice it stabilizes packs more tightly than the body-centered lattice of the 400 series — so 304 is 3.9% heavier than 410 at identical dimensions, and a part switched between the two families changes weight by 3.75% without a single dimension moving. 193 GPa. Slightly less stiff than carbon steel, and it work-hardens, so a formed stainless part springs back noticeably further.
What the magnet cannot do. It separates families and never grades. 304 and 316 are both austenitic, both non-magnetic annealed and, to the precision materials data publishes, the same density — the 2 to 3% molybdenum that makes 316 resist chlorides is the entire difference and it is invisible to every field test worth the name. If the distinction matters, and in marine or chloride service it does, it is a molybdenum spot test or a lab analysis, and the mill certificate is cheaper than either. Nor does a magnet say anything about condition: a 304 part that has been formed or machined will pull weakly along the worked areas and not at all elsewhere.
Where a stainless weight goes wrong next. None of these is a defined value. A density is a measured property of a commercial alloy, so treat every figure as a default you may override — the per-row 'varies' note says by how much and what moves it. Cast alloys carry porosity and weigh under the calculated figure; gray iron moves ±4% with its class. And the delivered weight of mill product differs from the calculated weight for a separate reason — see MILL_WEIGHT_TOLERANCE. Two specific traps sit past the density. Stainless sheet is stocked to the US Standard Gauge of 1893, whose weight column is wrought iron rather than stainless, which is a separate error from this one and belongs to the plate weight calculator. And stainless pipe is dimensioned by ASME B36.19M rather than B36.10M, so a schedule wall taken from the pipe weight calculator needs checking against the S-suffixed table before it is priced. Reference figures and arithmetic — material selection for a pressure, food-contact or marine application is an engineering decision, not a weight comparison.
How to weigh stainless when you are not certain of the grade
Family first, grade second, and the order quantity is what decides whether the difference is worth chasing.
Put a magnet on it before you look anything up
Nothing sticking means austenitic — the 300 series, at 8.00 g/cm³. Sticking hard means the 400 series, at 7.70. A weak pull in some places and not others is the interesting answer: cold work converts some austenite to martensite, so a formed flange, a sheared edge or a machined face on ordinary 304 will attract a magnet while the untouched middle of the same sheet will not. Test somewhere the material has not been worked.
Pick the grade, knowing the magnet only narrowed it to a family
304 and 316 are both austenitic, both non-magnetic annealed, and to the precision materials data publishes they are the same density — the 2 to 3% molybdenum that separates them is invisible on a scale and to every field test worth the name. Choose from the certificate, the purchase order or a spot test. The grade choice matters enormously for corrosion and not at all for this number.
Enter the whole order, not one length
Between 304 and 410 the difference is 3.75%, which is nothing on a bracket and is a pallet on a coil order. The page shows the same order costed both ways so the size of the question is visible before you decide whether it needs answering — and if it turns out to be a few pounds, that is a real answer too.
Technical specifications
| Grades carried | Three: 304/304L and 316/316L at 8.00 g/cm³ (0.28902 lb/in³) and martensitic 410 at 7.70 (0.27818), each with the ASTM A240 designation it comes from. |
|---|---|
| The gap that matters | 3.90% — austenitic against martensitic, the two crystal structures. On a 20,000 lb order that is 750 lb. Within the austenitic family the gap is nothing anybody publishes: 316 is sometimes given as 7.99 and sometimes 8.03. |
| Why the families differ | Nickel is denser than iron and stabilizes the face-centered cubic lattice, which packs at 74% against the body-centered 68% of the 400 series. The 400 grades have no nickel and a different structure, which is what makes them lighter and also what makes them hardenable. |
| Against carbon steel | 304 is 1.91% heavier than plain carbon steel at 7.85 g/cm³, and 410 is 1.91% lighter. A stainless part is not meaningfully heavier than the mild steel one it replaces — the reason to substitute is never mass. |
| Magnet test resolution | Family, not grade. It separates 300 series from 400 series reliably in annealed material, gives a false positive on cold-worked austenitic, and cannot distinguish 304 from 316 at all. That distinction is a molybdenum spot test or a lab. |
| Worked example | 1 in round bar is 2.7239 lb/ft in 304 and 2.6218 in 410. A 2 × 1/4 in flat bar is 1.7341 lb/ft in 304 against 1.7016 in carbon steel — a 1.9% difference on identical dimensions. |
| Mill forms | Six: sheet, plate and flat bar, round bar, hex bar, round and square tube, and hot-rolled angle. Tube is entered outside dimension and wall, as it is sold. |
| Where it runs | In this browser tab. No grade lookup, no order quantity and no dimension is sent anywhere. |
Frequently asked questions
My 304 sheet is slightly magnetic. Is it really 304?
Probably yes, and the magnetism is the forming rather than the grade. Austenitic stainless is metastable: deform it and some of the austenite transforms into martensite, which is ferromagnetic. So a bent flange, a deep-drawn corner, a sheared edge or a machined surface on ordinary 304 will pull a magnet while the undisturbed middle of the same sheet will not, and cold-rolled full-hard 301 can be strongly magnetic all over. The test is to check an area that has not been worked. If the whole piece attracts evenly and it was never formed, it is a 400 series grade after all, and it is 3.75% lighter than you priced it.
Is 316 heavier than 304?
By an amount nobody can measure on a purchase order. Both are published at 8.00 g/cm³, and the 2 to 3% molybdenum in 316 is denser than the iron it displaces, so some sources give 8.03 and others 7.99 — a spread of half a percent that is inside the variation between two heats of the same grade. Treat them as one density and spend the attention on the corrosion decision instead, where the difference is enormous: molybdenum is what makes 316 hold up in chlorides, which is why it is the marine and food-processing grade and 304 is not.
Why is 410 lighter than 304 if it is the harder grade?
Because hardness and density are unrelated properties, and the thing that makes 410 hardenable is exactly the thing that makes it lighter. 410 is martensitic: it has no nickel, its iron is in a body-centered structure, and that structure packs its atoms at about 68% of the available space against the face-centered austenitic 74%. Nickel itself is denser than iron, so the 300 series gains twice over. The same physics is why 410 can be heat treated to high hardness and 304 cannot — an austenitic grade work-hardens instead, and no amount of quenching will do anything to it.
Does a stainless part weigh much more than the mild steel one?
No — 1.91% for 304 and 1.91% less for 410, on identical dimensions. This surprises people who assume stainless is a heavy material, and it is worth stating because it removes weight from the substitution argument entirely. What actually changes when a part goes from carbon steel to stainless is cost, machinability, work hardening at the cutting edge, thermal expansion and galling behavior. Weight is the one property that stays effectively where it was, and a fabricator's crane, truck and rack calculations do not need redoing.
Which grade should I assume when the material is unmarked?
Assume nothing, run the magnet, and if the answer still matters get the certificate. Unmarked stainless in a rack is most often 304 because it is the most stocked grade on earth, but 'most often' is not a basis for a quote or a specification. The order of confidence goes: mill certificate, purchase order, magnet plus a plausible application, guess. If the guess has to happen, note that guessing austenitic is the conservative direction for weight — you will over-order by 3.75% rather than come up short — and the wrong direction for corrosion, since assuming 304 where a chloride environment needed 316 is a failure rather than an overspend.
Do polishing, passivation or a 2B finish change the weight?
Not by anything a calculation should carry. Passivation removes free iron from the surface and adds nothing. A 2B or BA finish is a rolling and annealing condition rather than a coating. Mechanical polishing to a No. 4 or No. 8 finish removes material rather than adding it, and on sheet that is a fraction of a thousandth. What does change the weight is the thickness tolerance the sheet arrived with: ASTM A480 permits a band that on thin material is a meaningful percentage, and it is why stainless coil is bought by weight and cut by the sheet.
How wrong is a calculator that offers one 'stainless' density?
Up to 3.9%, and you cannot tell which way without knowing which figure it picked. Most of them use 8.00 or its rounded imperial form and never say so, which means every 400 series job costed through them is over by 3.75% — the material comes up light against the invoice and somebody has to explain it. A few use 7.75 as an average of the families, which is wrong for everything and only slightly wrong for each. The fix is not a better average; it is asking which family, which is one magnet and one second of work.
About the two stainless families, and the test that separates them
The word stainless covers two metallurgies that behave differently in almost every respect, and weight is the one place the difference is a simple number. The austenitic 300 series — 304, 316, 321, 347 and the free-machining 303 — is iron with chromium and nickel in a face-centered cubic lattice, and it sits at 8.00 g/cm³. The martensitic and ferritic 400 series — 410, 416, 420, 430 — has no nickel and a body-centered lattice, and sits at 7.70. Two things stack up to make that 3.90% gap: nickel is denser than the iron it partly replaces, and the face-centered structure packs its atoms into about 74% of the available space against 68% for the body-centered one. The same structural difference decides everything else about the two families. The 400 series hardens by quenching and tempering, which is why it turns up as knife blades, valve trim and shafts; the 300 series cannot be hardened that way at all and work-hardens instead, which is why it galls on a thread and eats a dull tool.
All of which makes the magnet the most useful tool in this page, because it tests precisely the property the density difference comes from. Ferromagnetism follows the body-centered structure, so a 400 series part sticks to a magnet exactly as mild steel does and annealed austenitic does not. There are two things to know before trusting it. The first is the false positive: austenitic stainless is metastable, and cold work transforms some of its austenite into martensite, so a formed, sheared or machined surface on ordinary 304 pulls a magnet while the undisturbed material a few inches away does not — test somewhere nothing has happened to. The second is where the test simply stops: 304 and 316 are both austenitic and both non-magnetic, and the 2 to 3% molybdenum between them is invisible to any field method. For that you need a spot test, a lab, or the mill certificate, and in chloride service you need one of them rather than an assumption.
Two stainless weight errors live outside this page and are worth knowing about because they are larger than the grade question. Stainless sheet is stocked to the US Standard Gauge fixed in 1893, whose weight column was written for wrought iron at 480 lb/ft³ — so the number defining a stainless gauge is about 4% under what the sheet actually weighs, which the plate weight calculator prints alongside the real figure. And stainless pipe is dimensioned by ASME B36.19M rather than the B36.10M table the pipe weight calculator carries, so an S-suffixed schedule has to be checked before its wall is used. For everything else a shop buys — and for mixed orders where the stainless is one line among several — the metal weight calculator totals the lot, and if the part is going through a brake, remember that annealed 304 needs around 40% more tonnage than mild steel and springs back much further: that is the press brake tonnage calculator's territory. Material selection for pressure, food-contact or marine service is an engineering decision with somebody qualified signing it, not a density comparison.
Where these grade figures are worked out
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.