Dished End Weight, Blank Diameter & Volume Calculation Guide (Free Formulas + Chart)

Getting the dished end weight calculation right at the quotation stage saves EPCs and fabricators from costly surprises later — in material budgeting, transport planning, and crane/rigging selection. Yet most buyers either rely on a supplier's word or approximate blank diameter with guesswork. This guide gives you the exact formulas, a ready-reference chart, and a worked example so you can independently verify blank diameter, volume, and finished weight for torispherical, ellipsoidal, hemispherical, and conical dished ends — before you ever request a quote.

At KRR Dished Ends, we form heads up to 15 meters in diameter and 100+ mm thick across carbon steel, stainless steel, duplex, and exotic alloys like Hastelloy, Inconel, and Titanium. This guide reflects the same calculation logic our engineering team uses when preparing techno-commercial offers.

Why Blank Diameter & Weight Calculation Matters

The blank diameter is the size of the flat circular plate required before it is pressed or spun into a dished shape. Getting this number wrong has real consequences:

• Material cost overrun — an oversized blank wastes expensive alloy plate (critical for Hastelloy, Inconel, Titanium, and Duplex, where plate cost dominates the quote)

• Inaccurate freight and crane planning — underestimating finished weight can derail logistics for large-diameter heads

• Design mismatch — incorrect knuckle-to-crown proportions affect the head's pressure rating under ASME Section VIII

Below are the core formulas used across the industry, followed by a quick-reference chart and a fully worked calculation.

Blank Diameter Formula (General Method)

For most dished end types, blank diameter is estimated using:

Blank Diameter (BD) = Inside Diameter (ID) + 2 × Straight Flange (SF) + 2 × Head Depth Allowance

The "head depth allowance" changes based on the head profile:

Head Type	Approx. Depth Allowance (as a factor of ID)
Hemispherical	≈ 0.50 × ID
Ellipsoidal (2:1)	≈ 0.25 × ID
Torispherical (ASME F&D, L=ID, r=0.06 ID)	≈ 0.19–0.20 × ID
Conical (per included angle)	Varies with cone half-angle

Important: These are practical shop approximations widely used for budgetary estimates. Actual crown radius, knuckle radius, and forming allowance (spring-back, trim margin) shift the final blank size by a few percent. For a fabrication-ready blank diameter, our engineering team runs exact ASME Appendix 1-4 calculations as part of every formal quote — free of charge.

Volume Calculation Formulas by Head Type

Volume calculations are used for capacity sizing, hydro-test water volume, and coating/lining estimates. These are geometrically exact for the dish portion (excluding straight flange):

Hemispherical Head Volume = (π × ID³) / 12 ≈ 0.2618 × ID³

Ellipsoidal Head (2:1 ratio) Volume = (π × ID³) / 24 ≈ 0.1309 × ID³

Torispherical Head (ASME F&D, standard L=ID, r=0.06 ID) Volume ≈ 0.0809 × ID³ (compound curvature — verify with exact ASME tables for critical designs)

Conical Head Volume = (π/3) × R² × h, where R = ID/2 and h = cone height (based on half-angle)

(ID and results in the same length unit — e.g., ID in meters gives volume in cubic meters)

Weight Calculation Formula (With Material Density Chart)

Once the blank diameter is known, weight is calculated from the flat blank before forming:

Weight (kg) = 0.7854 × D² (mm) × Thickness (mm) × Density (kg/mm³)

Simplified for everyday use — Weight (kg) ≈ Factor × D² (in meters) × Thickness (in mm)

Material	Density (kg/m³)	Weight Factor
Carbon Steel	7,850	6.16
Stainless Steel (304/316)	8,000	6.28
Duplex / Super Duplex	7,800–7,850	6.13–6.16
Monel	8,830	6.94
Inconel	8,470	6.66
Hastelloy	8,890	6.98
Titanium	4,500	3.53
Aluminium	2,700	2.12

Example use: For a 3-meter blank diameter, 20 mm thick, in stainless steel: Weight = 6.28 × 3² × 20 = 6.28 × 9 × 20 ≈ 1,130 kg

Quick-Reference Chart: Blank Diameter & Weight at a Glance

ID (mm)	SF (mm)	Head Type	Approx. Blank Dia. (mm)	Thickness (mm)	Approx. Weight — CS (kg)
1,000	50	Torispherical	1,300	10	104
1,500	50	Torispherical	1,890	12	264
2,000	75	Ellipsoidal	2,650	16	692
3,000	75	Ellipsoidal	3,650	20	1,644
4,000	100	Torispherical	4,860	25	4,562
6,000	100	Ellipsoidal	6,900	32	9,376

Figures are indicative for carbon steel and rounded for quick reference. Actual figures vary with exact crown/knuckle radius and trim allowance — request a free precise calculation for your specification.

Worked Example: Step-by-Step Calculation

Given: Ellipsoidal (2:1) head, ID = 2,000 mm, thickness = 16 mm, straight flange = 75 mm, material = Stainless Steel 304.

Step 1 — Blank Diameter BD = ID + 2×SF + 2×(0.25×ID) = 2,000 + 150 + 1,000 = 3,150 mm

Step 2 — Volume (dish capacity) Volume = 0.1309 × (2.0 m)³ = 0.1309 × 8 = 1.047 m³

Step 3 — Weight Weight = 6.28 × (3.15)² × 16 = 6.28 × 9.92 × 16 ≈ 997 kg

This single head, before nozzles, cladding, or NDE allowances, weighs approximately 1 tonne — a figure that directly feeds into crane capacity and transport planning for the vessel fabricator.

Common Mistakes to Avoid

1. Ignoring straight flange (SF) in blank diameter — this alone can under-order plate by 100–150 mm on diameter

2. Using ellipsoidal formulas for torispherical heads (or vice versa) — the two profiles have significantly different depth allowances

3. Forgetting spring-back and trim allowance in cold-formed heads, especially in duplex and super duplex grades

4. Applying carbon steel density factors to alloy materials — Hastelloy and Inconel weigh 12–15% more than carbon steel at the same blank size

Why EPCs Trust KRR for Precision Dished Ends

KRR Dished Ends has been forming pressure vessel heads since 1976, certified under ASME, PED, PESO, PDIL, and EIL, and accredited across 12 countries. Our facility manufactures heads up to 15 meters in diameter and beyond 100 mm thickness, in carbon steel, stainless steel, duplex, super duplex, and exotic alloys including Hastelloy, Inconel, Monel, Titanium, and Tantalum.

Every enquiry we receive gets an exact, code-compliant blank diameter, volume, and weight calculation — not a rule-of-thumb estimate — as part of our formal techno-commercial offer.

Get a Free Precise Calculation & Quote →

Frequently Asked Questions

Q1. What is blank diameter in dished end manufacturing? Blank diameter is the size of the flat circular steel plate required before pressing or spinning it into the final dished (curved) shape. It includes the inside diameter, straight flange, and forming allowance for the head's curvature.

Q2. How is dished end weight calculated before forming? Weight is calculated on the flat blank using the formula: Weight = 0.7854 × Diameter² × Thickness × Material Density. This gives the plate weight consumed, which closely matches the finished head weight.

Q3. Does blank diameter change with material type? The blank diameter formula itself is geometric and does not change with material — but spring-back allowance varies slightly by material grade (duplex and higher-strength alloys need marginally more trim allowance than carbon steel).

Q4. Which head type requires the largest blank diameter for the same ID? For an identical inside diameter, hemispherical heads require the largest blank diameter, followed by ellipsoidal, then torispherical, due to their comparative depth of curvature.

Q5. Can KRR calculate exact blank diameter and weight for my specification? Yes. Share your ID, thickness, material grade, and design code (ASME/PED) through our quote page, and our engineering team will return exact calculations along with your techno-commercial offer.