Hole Volume Calculator

How to use the hole volume calculator

What this calculator does. This tool estimates the geometric volume of a circular cylindrical hole or a rectangular-prism hole. It also multiplies that volume by the number of holes and adds a user-selected waste allowance, producing a practical concrete-volume estimate. It does not determine structural footing size, soil bearing capacity, reinforcement, frost-depth compliance, or the suitability of a post foundation. Those decisions belong in a project design based on local requirements.

When to use it. Use the calculator to estimate concrete for fence-post holes, deck or pergola footings, small sign supports, or rectangular excavations that will be filled with concrete or another bulk material. It is also useful for comparing a round augered hole with a rectangular hand-dug excavation before ordering material.

How to calculate. The calculator opens with a ready-to-use demonstration: two circular holes, each 50 cm deep with a 10 cm radius, plus 7% waste. The example workbook is available immediately. To replace it:

1. Choose Hole shape: Circular or Rectangular.
2. Enter the dimensions and select a unit beside each measurement. For a circular hole, changing Radius automatically updates Diameter, and changing Diameter updates Radius.
3. Enter Number of holes, set the optional Waste allowance, and choose the Result unit.
4. Read the live result cards and the breakdown table, then use Download Excel to save the current validated model.
5. Use Reset to clear the demonstration and all calculated values. Download Excel becomes unavailable until a complete valid state is entered again.

Input guide. Depth is a required positive decimal measurement; enter a value such as 50 cm. Greater depth increases volume in direct proportion. Radius and Diameter are required for a circular hole; enter either one, such as 10 cm radius or 20 cm diameter. Since circular area depends on radius squared, doubling the radius quadruples the per-hole volume. A common mistake is entering the diameter as the radius. Length and Width are required only for a rectangular hole; values such as 80 cm by 40 cm are valid, and each changes volume proportionally. Number of holes must be a whole number from 1 to 10,000; fractions are rejected. Waste allowance is optional but must be from 0% to 100%; 5% to 10% is a common planning range, though job conditions vary. Result unit changes only the displayed and exported unit, not the physical quantity.

Output guide. Concrete volume including waste is the principal estimate for all holes. Volume per hole is the exact geometric volume for one idealized hole. Total before waste multiplies the per-hole value by the hole count. Waste volume is the added allowance, and it is zero when Waste allowance is 0%. Equivalent litres is always shown as a convenient cross-check. The breakdown table lists the same model values with their formula basis; it is an estimate rather than a purchase recommendation.

Worked example. For the startup circular hole, radius = 10 cm = 0.10 m and depth = 50 cm = 0.50 m. The per-hole volume is π × 0.10² × 0.50 = 0.015708 m³. Two holes require 0.031416 m³ before waste. Adding 7% gives 0.031416 × 1.07 = 0.033615 m³, equivalent to 33.615 litres. Those figures match the first-open result cards and Excel checkpoints.

Learn more. The geometric basis is the standard cylinder volume relationship for circular holes and the rectangular-prism volume relationship for box-shaped holes. For concrete planning and placement context, consult the Portland Cement Association guidance on placing concrete.