Tank Dimensions
⚡ Oval Cistern in 30 Seconds
Formula: π × a × b × h
a = half the length | b = half the width | h = height
Example: 8 ft long, 5 ft wide, 4 ft tall → a=4, b=2.5 → Volume = 3.14 × 4 × 2.5 × 4 = 125.6 ft³ → 940 gallons
Need this? Yes. Wrong size = waste money or run dry.
Volume (ft³) = 3.1416 × a × b × h
Gallons = ft³ × 7.48 | Liters = ft³ × 28.32
✅ 4 Steps to Get It Right
- Measure length and width. That's the oval top. Divide each by 2 to get a and b.
- Measure height (depth). Measure inside from bottom to top.
- Use same unit. All feet or all inches. Don't mix.
- Multiply. 3.14 × a × b × h = cubic feet. Then × 7.48 = gallons.
📐 Real Example (Step by Step)
Your tank: Length = 8 ft, Width = 5 ft, Height = 4 ft
Step 1: a = 8 ÷ 2 = 4 ft
Step 2: b = 5 ÷ 2 = 2.5 ft
Step 3: 3.14 × 4 × 2.5 × 4 = 125.6 ft³
Step 4: 125.6 × 7.48 = 940 gallons
Answer: 940 gallons. That's enough for a family of 4 for about 3 days.
🔄 Oval vs. Round vs. Rectangle
| Shape | Formula | Best for |
|---|---|---|
| Oval | π × a × b × h | Tight spaces, gardens |
| Rectangle | L × W × H | Most storage per footprint |
| Cylindrical | π × r² × h | Strength, rain harvesting |
📏 Common Oval Cistern Sizes
| Length × Width × Height | Gallons |
|---|---|
| 6' × 4' × 3' | ~423 |
| 8' × 5' × 4' | ~940 |
| 10' × 6' × 5' | ~1,764 |
| 12' × 8' × 6' | ~3,392 |
| 15' × 10' × 8' | ~7,065 |
📌 FAQ (Short Answers)
What's an oval cistern calculator?
It tells you how many gallons your oval tank holds. Formula: π × (L/2) × (W/2) × H.
Oval vs round – what's different?
Oval has two different radii (length and width differ). Round has one radius.
Can I use this for horizontal tanks?
Yes. Same formula. But height becomes the tank length. Calculator handles both.
Biggest mistake?
Using full length and width, not half. Remember: a = L/2, b = W/2. Not L and W.
What about domed or sloped bottoms?
This formula assumes flat bottom. For domed bottoms, estimate 70-80% of calculated volume.
💡 Pro Tips
- Add 20% buffer. Dry spells happen. Future needs grow.
- Measure inside. Tank walls steal space. Always measure inside.
- Plan for sediment. After 2-3 years, subtract 2-3 inches from height.
- Check local codes. Some areas require minimum fire storage.
💬 From Real Projects
Oval tanks fool people. They look big but hold less than a rectangle of same length and width. Run the numbers before you buy.
Half-diameter mistake is #1. I see it all the time. People plug in 8 ft instead of 4 ft. That gives 4x too much volume.
Measure twice. A 1 inch error on width = 30 gallons off on a 1,000 gal tank.
— Nasir, 10+ years excavation & water storage
Disclaimer: This calculator gives estimates. Real tanks vary. Always verify with your supplier.
© MultiTooSite — Real numbers, no fluff.
