Lay thickness for a 2-in compacted lift (dense-graded, 25%)
Loose thickness to lay: 2.67 in
- Loose thickness: 2 in ÷ (1 − 25/100) = 2.67 in
- Check: 2.67 in × (1 − 25/100) = 2 in compacted
Asphalt Compaction Calculator — Loose vs Compacted Thickness
A 2-inch compacted lift does not start at 2 inches — crews lay it looser and roll it down, about 25% for typical dense-graded mixes per the Asphalt Paving Handbook. Convert either direction with an editable rolldown, and keep one rule absolute: this never touches your tonnage.
The Formula
Compacted = Loose × (1 − Rolldown % ÷ 100) • Loose = Compacted ÷ (1 − Rolldown % ÷ 100)
How the Calculation Runs
- Compacted → loose: divide the target compacted thickness by (1 − rolldown/100).
- Loose → compacted: multiply the loose thickness by (1 − rolldown/100).
- The check step reverses the conversion to prove the pair is consistent.
- Tonnage is computed elsewhere from the compacted thickness only — this tool is display and planning, isolated from the order math by design.
What Each Variable Means
| Symbol | Variable | Unit | Notes |
|---|---|---|---|
| L | Loose thickness | in | Mat depth behind the paver screed, before rolling. |
| C | Compacted thickness | in | Finished depth after rolling — the number tonnage uses. |
| R | Rolldown factor | % | ≈25% dense-graded, ≈15% gap/open-graded (Handbook §7-5). Editable for your mix and rollers. |
Entering Your Numbers
- Convert
- Thickness (in)
- Rolldown (%) — Handbook §7-5: ≈25% for typical dense-graded mixes, ≈15% for gap/open-graded.
Known Limitations
- Rolldown is mix- and equipment-specific. The Handbook values are rules of thumb for typical mixes; your first rolled lift is the real calibration.
- This tool converts thickness only, by design. It intentionally produces no tonnage — see the isolation assumption below the result panel.
- Very thin lifts compact differently (less absolute rolldown in inches); thin-overlay specs should come from the mix designer.
- Loose-lay coefficients in field practice run about 1.15–1.4 depending on placement method (screed vs hand-laid vs vibratory) — from this project’s engineering knowledge base of municipal and highway paving plans, not a single public citation.
Worked Examples
Every number below is produced by the same engine at build time — not typed by hand.
A 3-in loose mat rolled at 20%
Compacted thickness achieved: 2.4 in
- Compacted thickness: 3 in × (1 − 20/100) = 2.4 in
- Check: 2.4 in ÷ (1 − 20/100) = 3 in loose
Frequently Asked Questions
What is the rolldown factor for asphalt?
The Asphalt Paving Handbook (§7-5) puts the common rolldown factor at approximately 25% for typical dense-graded mixes, and about 15% for gap/open-graded mixes. A 2-in compacted lift is therefore laid about 2.67 in loose.
How much does asphalt compact?
Dense-graded hot mix loses roughly a quarter of its loose thickness under rolling. The exact figure depends on mix design, lift thickness, temperature window, and roller type — measure your first lift to calibrate.
Should I add compaction to my tonnage?
No — that is the most common ordering mistake. Tonnage comes from compacted volume × compacted density. The loose mat is the same weight spread thicker; multiplying tons by a compaction factor counts it twice.
What thickness do I tell the paver crew?
Give them the loose thickness from the compacted → loose direction: target compacted depth ÷ (1 − rolldown). Screed setups and grade strings are set to the loose number; inspection measures the compacted one.
Sources & Data Lineage
- Asphalt Paving Handbook, Section 7-5 Layer Thickness — rolldown ≈25% dense-graded, ≈15% gap/open-graded. Reviewed 2026-09. handbook.asphaltpavement.org
- Asphalt Paving Handbook, Figure 109 — Rule of Thumb Rolldown Factor for Dense-Graded Mixtures. Reviewed 2026-09. handbook.asphaltpavement.org