Asphalt Compaction Calculator — Loose to Compacted Conversion
Loose asphalt behind the paver occupies about 20% more volume than the finished pavement. This calculator converts between loose and compacted thickness by mix type, and the page covers %Gmm acceptance bands, rolling patterns and the compaction problems that show up on site.
Asphalt compaction calculator
Enter your compacted design thickness and the calculator returns the tonnage, using the correct compaction factor for the mix you select. Use the table below to convert between loose and compacted thickness for setting a paver screed.
Compaction factors by mix
| Mix | Compaction factor | Volume reduction | Loose depth for 2" compacted |
|---|---|---|---|
| Dense-graded HMA | 1.20 | 17% | 2.40" |
| SMA | 1.18 | 15% | 2.36" |
| Warm mix asphalt | 1.20 | 17% | 2.40" |
| Open-graded friction course | 1.12 | 11% | 2.24" |
| Porous asphalt | 1.10 | 9% | 2.20" |
| Cold mix | 1.15 | 13% | 2.30" |
| RAP millings | 1.25 | 20% | 2.50" |
| Crushed stone base | 1.20 – 1.25 | 17–20% | 2.40–2.50" |
Compacted thickness = Loose thickness ÷ Compaction factor
Loose to compacted thickness
| Compacted target | Loose depth (HMA, factor 1.20) | Loose depth (RAP, 1.25) |
|---|---|---|
| 1" | 1.20" | 1.25" |
| 1.5" | 1.80" | 1.88" |
| 2" | 2.40" | 2.50" |
| 2.5" | 3.00" | 3.13" |
| 3" | 3.60" | 3.75" |
| 4" | 4.80" | 5.00" |
| 40 mm | 48 mm | 50 mm |
| 50 mm | 60 mm | 63 mm |
| 80 mm | 96 mm | 100 mm |
Order and specify against the compacted thickness. The loose figure only matters to the paver operator setting the screed. Calculating tonnage from a loose thickness over-orders by about 20%.
Density acceptance and %Gmm
| %Gmm achieved | Air voids | Assessment |
|---|---|---|
| under 90% | over 10% | Reject — mat is permeable and will ravel |
| 90 – 91.9% | 8–10% | Below spec on most contracts; pay reduction |
| 92 – 94% | 6–8% | Acceptable — typical lower specification bound |
| 94 – 96% | 4–6% | Target range on most highway work |
| 96 – 97% | 3–4% | Upper bound; approaching rutting risk |
| over 97% | under 3% | Over-compacted — flushing and rutting risk |
Compaction is normally paid on a sliding scale: full payment inside the target band, graduated reductions outside it, and removal and replacement below a floor value. On a large contract the difference between 93% and 95% average density is real money, which is why intelligent compaction systems that map coverage across the whole mat have become common.
Rolling patterns and equipment
| Stage | Equipment | Temperature | Purpose |
|---|---|---|---|
| Breakdown rolling | Steel double-drum vibratory | 240–290 °F | Achieves most of the density |
| Intermediate rolling | Pneumatic tyre roller | 200–240 °F | Kneads the surface, seals voids |
| Finish rolling | Steel drum, static | under 200 °F | Removes roller marks |
| Edge and detail | Vibratory plate or small roller | as available | Joints, edges and hand areas |
- Start at the low edge and work toward the high side so the mat is supported.
- Overlap each pass by about 6 inches or one third of the drum.
- Keep the drums wet but not flooded — excess water cools the mat.
- Never stop a vibrating roller on a hot mat. It leaves a permanent depression.
- Roll longitudinal joints first from the hot side, so the new mat is pushed into the cold one.
Common compaction problems
| Symptom | Cause | Fix |
|---|---|---|
| Roller marks that will not roll out | Mat too cool, or finish rolling started too late | Adjust rolling pattern timing |
| Shoving and displacement | Mat too hot, or unstable mix | Delay breakdown rolling; check mix design |
| Cracking under the roller | Mat too cool, or too thin for the aggregate size | Increase lift thickness or paving temperature |
| Low density at longitudinal joints | Joint rolled cold, or insufficient overlap | Roll from the hot side; use a joint heater |
| Density falls off at the edges | Unconfined edge | Use an edge restraint or roll the edge separately |
| Segregation — coarse patches | Truck loading or paver hopper practice | Use a material transfer vehicle; avoid emptying the hopper |
| Bleeding / flushing | Over-compaction or excess binder | Check mix design; reduce roller passes |
Frequently asked questions
What is the compaction factor for asphalt?
About 1.20 for dense-graded hot mix — loose material occupies 20% more volume than the compacted pavement. RAP millings are higher at about 1.25, porous asphalt lower at about 1.10.
How much does asphalt compact?
Roughly 15–25% by volume, depending on the mix. A 3 inch loose mat compacts to about 2.5 inches.
What is %Gmm?
The in-place bulk density expressed as a percentage of the theoretical maximum density with zero air voids. Specifications typically require 92–96%. Below 92% the mat is too porous; above 97% it is prone to rutting.
How thick should I lay asphalt to get 2 inches compacted?
About 2.4 inches loose for dense-graded hot mix at a compaction factor of 1.20. The paver screed is set to the loose thickness; the specification refers to the compacted result.
How many roller passes does asphalt need?
Typically 4–8 passes with a steel drum breakdown roller, followed by intermediate and finish rolling. The number depends on lift thickness, mix type and how fast the mat is cooling. Density testing, not pass counting, determines when it is done.
What happens if asphalt is under-compacted?
Air voids stay high, water and air get into the mat, the binder oxidises quickly and the surface ravels. Under-compaction is the single most common cause of premature asphalt failure and it is invisible on the day the job finishes.
Can asphalt be over-compacted?
Yes. Rolling beyond about 97% Gmm crushes aggregate and squeezes air voids too low, which makes the mix prone to rutting and flushing in hot weather.
Sources and further reading
- NAPA — National Asphalt Pavement Association
- AASHTO
- ASTM International
- FHWA — Federal Highway Administration
Related calculators and guides
Volume calculator
Loose and compacted volume.
Density guide
Gmm, Gmb and in-place density.
Thickness guide
Lift limits by aggregate size.
Tonnage calculator
Order quantity.
Millings calculator
Higher compaction factor.
Road layers
Compaction of each layer.