# Farm Pond Volume Calculator

> Find the water a dug farm pond holds from its top length and width, depth and side slope, in cubic metres, litres, cubic feet and US gallons.

Category: Agriculture · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/farm-pond-volume-calculator

A dug pond with sloping sides is an upside-down truncated pyramid. The prismoidal formula gives its exact volume from the top, middle and bottom areas.

Also called: Dugout volume calculator, Pond capacity calculator.

## Inputs
- Dimensions in (options: Metres, Feet; default m)
- Top length (at water level) (default 30)
- Top width (at water level) (default 20)
- Water depth (default 3)
- Side slope (horizontal : 1 vertical) (default 2)

## Results
- Pond volume
- Pond volume
- Pond volume (US gallons)
- Pond volume
- Bottom length
- Bottom width

## Formula

```
Bottom = Top − 2·z·d;  V = d ÷ 6 × (A_top + 4·A_mid + A_bottom)
```

Where:
- d: water depth
- z: side slope, horizontal per unit vertical
- A_top, A_bottom: areas of the water surface and the floor
- A_mid: area at half depth: (L − z·d)(W − z·d)

## Worked example
1. Bottom = (30 − 2×2×3) × (20 − 12) = 18 × 8 = 144 m².
2. Mid-depth = (30 − 6) × (20 − 6) = 24 × 14 = 336 m²; top = 600 m².
3. V = 3 ÷ 6 × (600 + 4×336 + 144) = 0.5 × 2,088 = 1,044 m³.

**Result:** A 30 × 20 m pond, 3 m deep with 2:1 sides, holds 1,044 m³, about 1.04 million litres.

## What the result means

Usable storage is less than the full volume: allow for evaporation, seepage and the dead storage below the pump intake. Measure dimensions at the water line you expect, not at the top of the bank.

## Assumptions and limits
- The pond is rectangular with the same slope on all four sides and a flat floor.
- Irregular or round ponds need to be approximated or surveyed.
- Sediment build-up reduces volume over time.

## Questions

### Why not just multiply length × width × depth?

With sloping sides that overstates the volume. For the example it would give 1,800 m³ instead of 1,044 m³.

### Is the prismoidal formula exact here?

Yes. For a straight-sided pit whose cross-section changes linearly with depth, the prismoidal formula gives the exact volume.

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Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/farm-pond-volume-calculator