Gravel Base Calculator for Concrete Slab

The calculator starts with finished compacted dimensions, converts that volume to cubic yards, and increases it by the allowance you enter to estimate loose delivered material. It then uses your supplier's tons-per-yard conversion and price per ton.

It does not select aggregate gradation, determine required base depth, evaluate soil, specify compaction, or include over-excavation beyond the dimensions entered. Geotextile, stabilization stone, drainage layers, trench backfill, and material extending beyond the slab must be calculated separately.

Calculate the compacted volume first, then increase it for settlement and compaction to obtain the loose delivered quantity. Convert yards to tons with the supplier's density.

The 15% allowance, 1.40 tons per cubic yard, and $45 price are editable examples. Use the quarry's conversion and current quote for the exact product and moisture condition being delivered.

• Remove organic soil, mud, and uncontrolled fill before placing aggregate.
• Use a compactable, well-graded material specified for slab base—not decorative rounded gravel unless approved.
• Place and compact in lifts appropriate for the equipment and material.
• Maintain drainage and verify final elevation before setting reinforcement and forms.
• Use geotextile or stabilization where the soil and design require it.

A slab base is an engineered layer, not simply any material sold as gravel. Well-graded angular aggregate generally compacts differently from clean open-graded stone or rounded decorative gravel. The correct material depends on drainage strategy, subgrade, loads, frost conditions, and the project specification.

• Ask for the exact product designation or gradation required by the drawings or local standard.
• Confirm whether the specified depth is compacted thickness and whether the base must extend beyond the slab edge.
• Keep topsoil, organics, mud, snow, frozen material, and construction debris out of the prepared section.
• Separate stabilization aggregate, capillary-break stone, leveling course, and ordinary base when the design uses more than one layer.

The percentage in this calculator is a purchasing allowance: it converts a compacted geometric volume into an estimated loose quantity. It is not a target density and does not prove that the installed base meets a specification.

Field acceptance may be based on material type, lift thickness, equipment, moisture, proof rolling, density testing, or another project requirement. Ask the designer or inspector what evidence is required before concrete placement.

• Quarries often sell by weight while landscape suppliers may quote by loose volume; confirm the billing unit before comparing prices.
• Request the supplier's tons-per-cubic-yard conversion for the named product rather than using a generic gravel value.
• Include delivery minimums, split-load restrictions, truck type, access, dumping location, and tax in the quote.
• Check whether the site can receive the truck without damaging utilities, pavement, septic components, landscaping, or overhead clearances.
• Order and compact a test quantity first when access, moisture, or an unfamiliar material makes yield uncertain.

Reviewed September 20, 2026. Primary references are linked directly below. Local codes, approved drawings, project specifications, geotechnical information, and supplier requirements take precedence.

• FHWA — Granular Base Application Description

  Federal Highway Administration guidance on aggregates used in granular base and subbase layers and material-performance considerations.

• FHWA — Field Materials Manual

  Primary federal field reference with chapters for aggregate base, subbase, stabilization, and concrete.

• ACI 360R — Guide to Design of Slabs-on-Ground

  Primary ACI reference addressing soil-support systems and slab design.

• QUIKRETE — Building a Concrete Patio

  Manufacturer project instructions illustrating compactible gravel subbase preparation beneath residential flatwork.