How do I calculate the weight of a steel plate?

Multiply thickness in millimetres by 7.85 to get kilograms per square metre, then multiply by the plate area in square metres. A 2 m × 1 m plate of 10 mm steel weighs 10 × 7.85 × 2 = 157 kg. In imperial units, thickness in inches × 40.8 gives pounds per square foot. Both figures assume carbon steel at 7.85 g/cm³.

What is the difference between plate and sheet?

The boundary is conventional rather than metallurgical. In North America, steel 3/16 in (4.76 mm) and thicker is plate; anything thinner is sheet. The distinction matters because plate and sheet are governed by different specifications, stocked in different thickness series and cut with different processes — sheet is sheared or laser-cut, heavy plate is flame-cut or plasma-cut.

Is 6 mm plate the same as 1/4 inch plate?

No. 1/4 in is 6.35 mm, so 6 mm plate is about 5.5% thinner. For a bracket or a cover the substitution is usually harmless, but where the thickness was calculated for a bending load or a pressure boundary the reduction in section modulus matters — bending stiffness scales with the cube of thickness, so a 5.5% reduction in thickness costs roughly 16% of stiffness.

Why is my 10 mm plate measuring 9.7 mm?

Because that is within the permitted rolling tolerance. Hot-rolled plate is supplied to a negative thickness allowance that grows with nominal thickness and plate width, so a nominal 10 mm plate measuring 9.7 mm can be fully compliant. If thickness is critical, order to a restricted tolerance class, or specify that the plate be machined to thickness after rolling.

Steel Plate Sizes

Standard structural steel plate thicknesses in both metric and imperial series, with mass per unit area for each — the number you need to convert a plate area into a weight.

Data verified 2026-09-29 · based on ASTM A6/A6M-24

Quick Answer

Steel plate runs from about 3 mm (1/8 in) to 400 mm in standard mill stock. Weight is simple arithmetic: kg/m² = 7.85 × thickness in mm, so a 10 mm plate weighs 78.5 kg/m² and a 1 inch plate weighs 40.8 lb/ft². Rolling tolerance means the delivered plate is usually slightly under nominal thickness.

Find a thickness

Standard Steel Plate Thicknesses and Unit Weight

Thickness mm^[1]	Thickness in^[3]	Weight kg/m²^[4]	Weight lb/ft²^[5]	Series and availability^[1]
3.175 #	0.1250	24.92	5.10	Imperial — 1/8 in — light plate, sheet-like handling
4.763 #	0.1875	37.39	7.66	Imperial — 3/16 in — the lightest common structural plate
5 #	0.1969	39.25	8.04	Metric — Metric preferred number
6 #	0.2362	47.10	9.65	Metric — Metric preferred number; also 1/4 in equivalent stock
6.35 #	0.2500	49.85	10.21	Imperial — 1/4 in
7.938 #	0.3125	62.31	12.76	Imperial — 5/16 in
8 #	0.3150	62.80	12.86	Metric — Metric preferred number
9.525 #	0.3750	74.77	15.31	Imperial — 3/8 in
10 #	0.3937	78.50	16.08	Metric — Metric preferred number
11.113 #	0.4375	87.24	17.87	Imperial — 7/16 in
12 #	0.4724	94.20	19.29	Metric — Metric preferred number
12.7 #	0.5000	99.69	20.42	Imperial — 1/2 in
15 #	0.5906	117.75	24.12	Metric — Metric preferred number
15.875 #	0.6250	124.62	25.52	Imperial — 5/8 in
16 #	0.6299	125.60	25.72	Metric — Metric preferred number
19.05 #	0.7500	149.54	30.63	Imperial — 3/4 in
20 #	0.7874	157.00	32.16	Metric — Metric preferred number
22.225 #	0.8750	174.47	35.73	Imperial — 7/8 in
25 #	0.9843	196.25	40.20	Metric — Metric preferred number
25.4 #	1.0000	199.39	40.84	Imperial — 1 in
30 #	1.1811	235.50	48.23	Metric — Metric preferred number
31.75 #	1.2500	249.24	51.05	Imperial — 1 1/4 in
38.1 #	1.5000	299.08	61.26	Imperial — 1 1/2 in
40 #	1.5748	314.00	64.31	Metric — Metric preferred number
50 #	1.9685	392.50	80.39	Metric — Metric preferred number
50.8 #	2.0000	398.78	81.68	Imperial — 2 in
60 #	2.3622	471.00	96.47	Metric — Metric preferred number
63.5 #	2.5000	498.47	102.10	Imperial — 2 1/2 in
76.2 #	3.0000	598.17	122.51	Imperial — 3 in
80 #	3.1496	628.00	128.62	Metric — Metric preferred number
100 #	3.9370	785.00	160.78	Metric — Metric preferred number
101.6 #	4.0000	797.56	163.35	Imperial — 4 in
127 #	5.0000	996.95	204.19	Metric — Metric preferred number
152.4 #	6.0000	1196.34	245.03	Imperial — 6 in
203.2 #	8.0000	1595.12	326.71	Imperial — 8 in
254 #	10.0000	1993.90	408.38	Imperial — 10 in — heavy plate, mill availability limited
304.8 #	12.0000	2392.68	490.06	Imperial — 12 in — heavy plate, mill availability limited
400 #	15.7480	3140.00	643.12	Metric — Heavy plate, mill availability limited

Weights are calculated at 7.85 g/cm³, the standard figure for carbon and low-alloy steel. Stainless steel is about 2% heavier (7.9–8.0 g/cm³) and aluminium is roughly 35% lighter (2.70 g/cm³) — use the density of the actual material, not this table, for anything other than steel. Weights ignore rolling tolerance: plate is generally supplied at or slightly below nominal thickness, so the delivered weight per unit area is usually a fraction of a percent under the figure shown.

Two Plate Series, and Why Both Exist

Structural plate is stocked in two thickness series that do not line up. The imperial series, governed in North America by ASTM A6, is built on fractions of an inch — 3/16, 1/4, 5/16, 3/8 and so on up to 1 inch, then quarter-inch steps above it. The metric series, governed in Europe by EN 10025-2, is built on preferred numbers — 5, 6, 8, 10, 12, 15, 20, 25, 30, 40, 50 mm and upwards.

The two only coincide at 25.4 mm and 1 inch. A 6 mm plate is 0.2362 in, and a 1/4 in plate is 6.35 mm — close enough to confuse a specification and not close enough to substitute. When a drawing calls for 1/4 in plate and the yard stocks 6 mm, the substitution is a 1.6% thickness reduction and a corresponding loss of section modulus; it is usually acceptable for a bracket, and it is not acceptable where the plate thickness was calculated for a pressure or a bending load.

Above roughly 100 mm the two series diverge further and availability narrows. Plate over 150 mm is a mill order in most markets, not a stock item, and heavy plate is usually supplied to a minimum order quantity with a lead time measured in weeks.

Rolling Tolerance, and Why Plate Is Rarely Nominal

A plate ordered as 10 mm is not 10.00 mm thick. Hot rolling leaves the thickness slightly under nominal, and the permitted deviation is defined by the specification rather than by the mill's discretion.

Under ASTM A6, the permitted under-thickness allowance grows with nominal thickness and with the width of the plate — a narrow strip is rolled to a tighter tolerance than a wide one. EN 10025-2 sets its own limits, again depending on thickness range and whether the plate is ordered to a restricted tolerance class. The practical consequence is that a plate can be a few tenths of a millimetre thin and still be fully compliant, which is why plate is a poor choice of stock for a part where thickness sets the finished dimension.

Two further cautions. Crown — a slight thickening at the centre of the plate — means thickness varies across the width, so a measurement at the edge is not the thickness at the middle. And flame-cut or plasma-cut edges are not square to the face and carry a heat-affected zone; a part that must be square on all six faces needs the edges machined, not just cleaned up.

Frequently Asked Questions

How do I calculate the weight of a steel plate?: Multiply thickness in millimetres by 7.85 to get kilograms per square metre, then multiply by the plate area in square metres. A 2 m × 1 m plate of 10 mm steel weighs 10 × 7.85 × 2 = 157 kg. In imperial units, thickness in inches × 40.8 gives pounds per square foot. Both figures assume carbon steel at 7.85 g/cm³.
What is the difference between plate and sheet?: The boundary is conventional rather than metallurgical. In North America, steel 3/16 in (4.76 mm) and thicker is plate; anything thinner is sheet. The distinction matters because plate and sheet are governed by different specifications, stocked in different thickness series and cut with different processes — sheet is sheared or laser-cut, heavy plate is flame-cut or plasma-cut.
Is 6 mm plate the same as 1/4 inch plate?: No. 1/4 in is 6.35 mm, so 6 mm plate is about 5.5% thinner. For a bracket or a cover the substitution is usually harmless, but where the thickness was calculated for a bending load or a pressure boundary the reduction in section modulus matters — bending stiffness scales with the cube of thickness, so a 5.5% reduction in thickness costs roughly 16% of stiffness.
Why is my 10 mm plate measuring 9.7 mm?: Because that is within the permitted rolling tolerance. Hot-rolled plate is supplied to a negative thickness allowance that grows with nominal thickness and plate width, so a nominal 10 mm plate measuring 9.7 mm can be fully compliant. If thickness is critical, order to a restricted tolerance class, or specify that the plate be machined to thickness after rolling.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	ASTM A6/A6M — General Requirements for Rolled Structural Steel Bars, Plates, Shapes and Sheet Piling	standard	ASTM A6/A6M-24 — source
[2]	EN 10025-2 — Hot rolled products of structural steels, technical delivery conditions	standard	EN 10025-2:2019
[3]	Metric thickness converted from the imperial figure	derived	t(mm) = t(in) × 25.4, using the international inch of exactly 25.4 mm. Rounded to three decimals.
[4]	Mass per unit area	derived	m/A = t × ρ, with t in mm and ρ = 7.85 g/cm³ = 7.85 kg/m² per mm of thickness, so kg/m² is numerically 7.85 × t(mm). Ignores rolling tolerances, which for plate are typically −0.3 mm to +0.8 mm depending on the specification.
[5]	Imperial mass per unit area	derived	lb/ft² = kg/m² × 0.204816, the exact conversion between kilograms per square metre and pounds per square foot.
[6]	Density of carbon and low-alloy steel	standard	n/a — long-established physical constant; 7.85 g/cm³ is the value used throughout this site for steel

Data Sources

Standard	Revision	What it covers on this page
ASTM A6/A6M — General Requirements for Rolled Structural Steel Bars, Plates, Shapes and Sheet Piling	ASTM A6/A6M-24	the imperial plate thickness series and the permitted thickness tolerances
EN 10025-2 — Hot rolled products of structural steels	EN 10025-2:2019	the metric plate thickness series and its tolerances
Density of steel, 7.85 g/cm³	n/a — physical constant, not a revisioned document	every weight figure in the table

Cross-checked against:

Thickness series checked against published mill stock lists for both metric and imperial plate
Unit weights cross-checked against published steel plate weight tables — the 1 inch figure of 40.8 lb/ft² agrees
Every unit conversion on the page is re-derived arithmetically at build time and compared against the printed value

Derived values — the following values on this page are calculated, not taken directly from the standard:

Value	How it is derived
Thickness in inches	t(mm) ÷ 25.4, using the international inch of exactly 25.4 mm, rounded to four decimals. Every value is recomputed at build time and compared against the printed figure to within 0.2%.
Weight in kg/m²	m/A = 7.85 × t(mm), from a steel density of 7.85 g/cm³. Checked at build time against the printed value to within 0.2%, and spot-checked against the published figures 78.5 kg/m² for 10 mm and 196.25 kg/m² for 25 mm.
Weight in lb/ft²	kg/m² × 0.204816, the exact kilogram-per-square-metre to pound-per-square-foot conversion. The 1 inch plate value of 40.8 lb/ft² is held as a known value check against the published figure.

Thicknesses are nominal and weights are calculated at the standard steel density of 7.85 g/cm³; delivered plate is normally at or slightly below nominal thickness, and stainless or aluminium plate differs substantially. Use these figures for estimating, take-off and stock selection, and the actual material's certified density for a weight-critical design.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Steel Plate Sizes." https://refmanual.com/charts/steel-plate-sizes/ (accessed 2026-09-29). Data from ASTM A6/A6M — General Requirements for Rolled Structural Steel Bars, Plates, Shapes and Sheet Piling, ASTM A6/A6M-24.

BibTeX

@misc{steel-plate-sizes,
  title        = {Steel Plate Sizes},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/steel-plate-sizes/}},
  note         = {Accessed: 2026-09-29},
  source       = {ASTM A6/A6M — General Requirements for Rolled Structural Steel Bars, Plates, Shapes and Sheet Piling, ASTM A6/A6M-24}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Steel Plate Sizes
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/steel-plate-sizes/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ASTM A6/A6M — General Requirements for Rolled Structural Steel Bars, Plates, Shapes and Sheet Piling, ASTM A6/A6M-24
ER  -

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