Water Tank Capacity Calculator – Tank Volume, Litres & Gallons Guide

Water Tank Capacity Calculator – Tank Volume, Litres & Gallons Guide

Calculate cylindrical and rectangular water tank capacity instantly. Convert between litres, gallons, and cubic metres. Estimate domestic, commercial, and rainwater harvesting storage requirements using engineering-grade formulas, sizing charts, and interactive tools trusted by plumbing engineers and building services professionals.

πŸ”§ Calculate Tank Capacity πŸ“Š Compare Tank Sizes πŸ”„ Convert Litres & Gallons πŸ“– View FAQ Guide
CAPACITY Hβ‚‚O

πŸ”§ Interactive Water Tank Capacity Calculator

Select tank shape, enter dimensions, and instantly calculate volume in litres, gallons, and cubic metres.

πŸ“

Cylindrical Tank Volume Calculator

1,696
Litres (L)
448
US Gallons
373
UK Gallons
1.696
Cubic Metres (mΒ³)
100%
πŸ“

Cylindrical Tank Formula

Volume = Ο€ Γ— rΒ² Γ— h

// Where:
r = radius = diameter Γ· 2
h = height of the tank
Ο€ β‰ˆ 3.14159

// Conversion:
1 mΒ³ = 1000 litres
1 mΒ³ = 264.172 US gallons
1 mΒ³ = 219.969 UK gallons
πŸ’‘ Engineering Note: For horizontal cylindrical tanks, the volume at partial fill uses a more complex formula involving the circular segment area. Our calculator handles both vertical and horizontal orientations automatically.

Related: Cylinder Volume Calculator β€’ Tank Volume Formula Guide β€’ Water Storage Sizing Guide

πŸ“¦

Rectangular Tank Volume Calculator

2,400
Litres (L)
634
US Gallons
528
UK Gallons
2.400
Cubic Metres (mΒ³)
πŸ“

Rectangular Tank Formula

Volume = Length Γ— Width Γ— Height

// Where all dimensions are in metres:
V = L Γ— W Γ— H

// Example (2m Γ— 1m Γ— 1.2m):
V = 2.0 Γ— 1.0 Γ— 1.2 = 2.4 mΒ³
V = 2400 litres
πŸ—οΈ Underground Tank Sizing: Rectangular tanks are commonly used for underground water storage. Ensure the tank is rated for hydrostatic pressure and soil loading. Allow minimum 300mm clearance around all sides for installation access.

Related: Water Tank Volume Calculator β€’ Pipe Volume Calculator β€’ Water Weight Calculator

🏠

Domestic Water Demand Estimator

600
Daily Demand (L/day)
Recommended Tank (Litres)
4,200
Weekly Demand (Litres)
1.8
Cubic Metres (mΒ³)
πŸ“‹ Sizing Recommendation: For a 3-bedroom house with 4 occupants, a 1,800-2,000 litre water tank is recommended for 3 days of backup storage.
🌧️

Rainwater Harvesting Tank Sizing Calculator

61,200
Annual Collection (Litres)
5,100
Recommended Tank (Litres)
5,100
Avg Monthly (Litres)
Β£183
Est. Annual Savings*
πŸ’§ Sustainable Storage: Rainwater harvesting can reduce mains water consumption by 30-50% for domestic properties. Ensure proper filtration and overflow systems are installed. Check local regulations for rainwater harvesting incentives.

*Estimated at Β£3.00/mΒ³ water cost. Actual savings vary by region.

πŸ“Š Water Tank Capacity Chart – Standard Sizes & Dimensions

Comprehensive reference table for common water tank sizes with typical dimensions and applications.

Tank Shape Capacity (Litres) Capacity (US Gal) Capacity (UK Gal) Cubic Metres Height / Length Diameter / Width Typical Usage
Cylindrical Vertical 250 L 66 US gal 55 UK gal 0.25 mΒ³ 1.2 m 0.55 m Domestic Loft
Cylindrical Vertical 500 L 132 US gal 110 UK gal 0.50 mΒ³ 1.5 m 0.70 m Small Home
Cylindrical Vertical 1,000 L 264 US gal 220 UK gal 1.0 mΒ³ 1.8 m 0.90 m Family Home
Cylindrical Vertical 2,000 L 528 US gal 440 UK gal 2.0 mΒ³ 2.2 m 1.15 m Large House
Cylindrical Vertical 5,000 L 1,321 US gal 1,100 UK gal 5.0 mΒ³ 2.8 m 1.60 m Commercial
Cylindrical Vertical 10,000 L 2,642 US gal 2,200 UK gal 10.0 mΒ³ 3.5 m 2.00 m Office Building
Cylindrical Horizontal 2,000 L 528 US gal 440 UK gal 2.0 mΒ³ 2.5 m (length) 1.10 m Rainwater
Rectangular 1,000 L 264 US gal 220 UK gal 1.0 mΒ³ 1.5 Γ— 1.0 m 0.70 m (h) Underground
Rectangular 5,000 L 1,321 US gal 1,100 UK gal 5.0 mΒ³ 2.5 Γ— 2.0 m 1.00 m (h) Hotel/Guesthouse
Rectangular 20,000 L 5,283 US gal 4,399 UK gal 20.0 mΒ³ 5.0 Γ— 3.0 m 1.35 m (h) Factory/School

πŸ”„ Unit Conversion – Litres, Gallons & Cubic Metres

Quick reference conversion table for water storage volume units commonly used in hydraulic engineering.

From To Litres To US Gallons To UK Gallons To Cubic Metres
1 Litre1.0 L0.264 US gal0.220 UK gal0.001 mΒ³
1 US Gallon3.785 L1.0 US gal0.833 UK gal0.00379 mΒ³
1 UK Gallon4.546 L1.201 US gal1.0 UK gal0.00455 mΒ³
1 Cubic Metre1,000 L264.17 US gal219.97 UK gal1.0 mΒ³
1 Cubic Foot28.32 L7.48 US gal6.23 UK gal0.0283 mΒ³

πŸ“ Worked Engineering Examples

Step-by-step calculations demonstrating real-world water tank sizing scenarios.

1️⃣

Domestic 1000L Cylindrical Tank

// Given: Need 1000L, diameter 0.9m
V = Ο€ Γ— rΒ² Γ— h
1000L = Ο€ Γ— (0.45)Β² Γ— h
h = 1000 / (Ο€ Γ— 0.2025 Γ— 1000)
h β‰ˆ 1.57 metres
// Tank: Ø0.9m Γ— 1.6m tall β‰ˆ 1018L
2️⃣

Rainwater Harvesting – 100mΒ² Roof

// Annual rainfall: 800mm
Collection = Area Γ— Rainfall Γ— Coeff Γ— Efficiency
= 100mΒ² Γ— 0.8m Γ— 0.85 Γ— 0.90
= 61.2 mΒ³/year
= 61,200 litres/year
// Recommend 5000L tank (1 month storage)
3️⃣

Commercial Office – 50 Occupants

// 50 people Γ— 45L/day (office use)
Daily demand = 50 Γ— 45 = 2,250 L
// 3-day backup
Storage = 2,250 Γ— 3 = 6,750 L
// Select: 7000-10000L tank
4️⃣

Underground Rectangular Tank

// Excavation: 3m Γ— 2m Γ— 1.5m deep
V = L Γ— W Γ— H
= 3.0 Γ— 2.0 Γ— 1.5
= 9.0 mΒ³ = 9,000 litres
// Allow 200mm for structure = 8.4mΒ³ usable

πŸ—οΈ Water Tank Installation & Sizing Requirements

Essential engineering considerations for water storage tank specification and installation.

πŸ”©

Domestic Water Tank Sizing Guide

  • Apartment/Flat: 250–500L (loft tank)
  • 2-Bedroom Home: 1,000–1,500L
  • 3-Bedroom House: 1,500–2,500L
  • 4-Bedroom Family Home: 2,500–5,000L
  • Large/Multi-Gen Home: 5,000L+
  • Emergency Backup: Allow 3–7 days storage
  • Potable Water: Must meet BS 8558 / local regs
🏒

Commercial Water Tank Sizing

  • Office Building: 45L/person/day
  • Schools: 15–30L/pupil/day
  • Hotels: 200–300L/guest/day
  • Factories: 60–100L/worker/day
  • Hospitals: 300–500L/bed/day
  • Backup Storage: Minimum 24–48 hours
  • Fire Storage: Additional capacity per BS 9251
πŸ› οΈ

Installation Requirements

  • Tank Base: Level concrete plinth, min 150mm thick
  • Structural Support: Rated for full water weight (1L = 1kg)
  • Overflow System: Minimum same diameter as inlet
  • Access: 600mm clearance around all sides
  • Ventilation: Screened overflow & vent pipe
  • Insulation: Required for outdoor/loft installations
  • Potable Regulations: WRAS-approved materials (UK)
πŸ“

Key Engineering Parameters

  • Hydrostatic Pressure: 9.81 kPa per metre of head
  • Static Head: Height from tank outlet to highest fixture
  • Flow Rate: Minimum 15–25 L/min for domestic
  • Storage Efficiency: ~90% usable (allow dead storage)
  • Thermal Expansion: Allow 2% volume for temperature changes
  • Material Options: GRP, PE, Stainless Steel, Concrete

❓ Frequently Asked Questions – Water Tank Capacity & Sizing

Expert answers to the most common water storage engineering questions.

Continue your hydraulic engineering calculations with these specialized tools.

πŸ“ Water Tank Volume Calculator β†’ πŸ”΅ Cylinder Volume Calculator β†’ πŸ”§ Pipe Volume Calculator β†’ πŸ’ͺ Water Pressure Calculator β†’ 🌊 Pipe Flow Rate Calculator β†’ πŸ“Š Flow Rate Calculator β†’ βš–οΈ Water Weight Calculator β†’ 🚿 Fixture Unit Calculator β†’ πŸ”₯ Hot Water Cylinder Sizing β†’ πŸ’· Heating Cost Calculator β†’ ⚑ Energy Efficiency Calculator β†’ 🌑️ Pipe Heat Loss Calculator β†’ 🌧️ Rainwater Harvesting Calculator β†’ πŸ“– Water Storage Sizing Guide β†’ πŸ“ Tank Volume Formula Guide β†’

πŸ“‹ Water Storage Engineering Summary

Proper water tank sizing is fundamental to hydraulic engineering, plumbing system design, and sustainable water management. Whether you're specifying a domestic cold water storage tank, designing a commercial rainwater harvesting system, or calculating underground water storage capacity, accurate volume calculations ensure system reliability, regulatory compliance, and cost-effective installation. Use our water tank capacity calculator above to determine your exact requirements, consult the tank capacity charts for standard sizing, and refer to the engineering formulas for custom tank geometries. For complex projects, always consult a qualified building services engineer or plumbing design professional.

Last updated: May 2026. All calculations follow standard hydraulic engineering principles. Always verify against local building codes and water regulations.

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