Measure the patch after its edges are squared to sound pavement, not while the hole still shows its ragged outline. The visible pothole understates the repair because the squared boundary runs past the broken edge to solid pavement. A measurement taken from the ragged outline will order short and leave the new edge sitting on failed material.
One patch needs four recorded figures: length, width, average depth, and hole volume. Maximum depth goes on the record beside the average because it decides how the fill is placed. Everything else on the page supports those four figures.
What do you measure, and when?
Measure after marking and cutting, once loose material and standing water are out of the hole and the base is exposed. A depth reading taken through loose rubble measures rubble, not the hole. A length taken across crumbling edge measures pavement that will be cut away anyway.
Record one patch per row. A driveway with three holes is three rows, not one combined figure, because each hole has its own depth and its own base condition.
| Field | What to write | Fixture A entry |
|---|---|---|
| Location | Driveway, lane, or lot bay, plus a sketch reference | Driveway apron, left wheel track |
| Patch shape | Rectangle, or the rectangles it was split into | One rectangle |
| Length and width | Measured sides of the squared patch, in one unit | 48 in by 36 in |
| Depth readings | Every reading, not only the average | 2.5, 3, 3.5, 2 in |
| Average depth | Sum of readings divided by reading count | 2.75 in |
| Maximum depth | Deepest single reading | 3.5 in |
| Hole volume | Area times average depth, in cubic feet and cubic yards | 2.75 ft3, 0.102 yd3 |
| Base condition | Firm, soft, wet, or pumping, as observed | Firm and dry |
Mark and square the patch first
Caltrans maintenance guidance for semi-permanent patching marks the boundary slightly larger than the visible distress, as rectangular as possible, and cuts it square with a diamond saw or a pneumatic hammer with a spade bit. The sides are then squared until the edges stand in sound pavement over firm supporting material. The guidance also suggests making the patch depth 50 percent thicker than the failed layer, which is a repair-depth suggestion for the crew, not a number the measurer invents on site.
The FHWA semi-permanent procedure behind the Pavement Interactive summary states the same edge rule in plainer terms: remove water and debris, square the sides so they are vertical, and keep intact pavement on all sides. Vertical sides matter for measurement because a sloped edge has no single length or width. A squared hole is a rectangular prism, and a rectangular prism has one volume formula.
Mark the boundary, cut it, clear it, and only then pick up the tape. Any measurement taken before that sequence describes a hole that no longer exists once the saw has passed.
Measure length and width
Measure the two sides of the squared rectangle in the same unit, inches or feet, and write the unit beside each figure. Mixing units inside one patch is the most common source of a volume error that looks correct: 48 and 3 can mean 48 inches by 3 feet, or 48 feet by 3 inches, and the two holes differ by a factor of 144.
Area = length x width
Fixture A is one rectangle, 48 inches long and 36 inches wide. Convert each side to feet first: 48 / 12 = 4 ft, and 36 / 12 = 3 ft. Area is 4 x 3 = 12 ft2. In square yards, 12 / 9 = 1.333 yd2, shown as 1.33 yd2.
An irregular patch is split into rectangles, measured one at a time, and added. Fixture B is an L-shaped patch split into two rectangles. Rectangle 1 measures 60 inches by 24 inches, which is 5 ft by 2 ft, giving 10 ft2. Rectangle 2 measures 24 inches by 24 inches, which is 2 ft by 2 ft, giving 4 ft2. Total area is 10 + 4 = 14 ft2.
The split method also guards against the bounding-rectangle error. One rectangle drawn around the whole of fixture B would measure 60 inches by 48 inches, giving 20 ft2. That figure overstates the patch by 6 ft2, and every later figure built on it, including volume and any purchase quantity, inherits the overstatement.
Measure depth with several readings
Depth varies more than length or width across one hole, because the base is uneven and the failed layer thins at the edges. One reading at the centre can miss a deep pocket at one corner and a shallow shelf at another. Take readings at the corners and near the centre, clear of loose material, and write down every reading before averaging.
Fixture A uses four readings: 2.5, 3, 3.5, and 2 inches. The average is (2.5 + 3 + 3.5 + 2) / 4 = 11 / 4 = 2.75 inches. The average drives the volume figure because it represents the whole hole. The maximum, 3.5 inches, stays on the record beside it because it flags the deep pocket and sets the lift plan below.
Use the average for volume and the maximum for placement. Using the maximum for volume would overstate the hole, since most of the patch is shallower than its deepest point. Using the average alone, without recording the maximum, would hide the pocket that needs its own lift.
Convert area and depth to volume
Volume is area times average depth, with both figures in matching units. Convert depth to feet when area is in square feet, or work entirely in inches and convert at the end. Either route gives the same volume when the conversions are applied once.
Volume = area x average depth
| Conversion | Rule | Fixture A check |
|---|---|---|
| Inches to feet | Divide by 12 | 48 in = 4 ft; 2.75 in = 0.22917 ft |
| Square feet to square yards | Divide by 9 | 12 ft2 = 1.33 yd2 |
| Cubic inches to cubic feet | Divide by 1,728 | 4,752 in3 = 2.75 ft3 |
| Cubic feet to cubic yards | Divide by 27 | 2.75 ft3 = 0.102 yd3 |
Fixture A, worked in full: area 12 ft2 times average depth 0.22917 ft gives 2.75 ft3. The cubic-inch cross-check gives the same result: 48 x 36 x 2.75 = 4,752 in3, and 4,752 / 1,728 = 2.75 ft3. In cubic yards, 2.75 / 27 = 0.10185 yd3, shown as 0.102 yd3.
Fixture B, worked in full: area 14 ft2 times average depth 3 inches, which is 0.25 ft, gives 3.5 ft3. In cubic yards, 3.5 / 27 = 0.12963 yd3, shown as 0.130 yd3.
Fixture C is a metric check: a patch 1.2 m by 0.9 m gives 1.08 m2. Average depth 70 mm is 0.07 m. Volume is 1.08 x 0.07 = 0.0756 m3. The method is identical; only the conversion factors change.
Work fixture A in feet and again in cubic inches. Two routes that land on 2.75 ft3 confirm the arithmetic. Two routes that disagree mean a conversion was applied twice or skipped, and the disagreement is cheaper to find at the desk than at the curb.
Turn depth into a lift count
Patch material is placed in lifts, and each lift is compacted before the next goes on. The lift limit belongs to the product label, so read it before counting lifts. The PRO-ROAD cold mix sheet sets lifts at a maximum of 5 cm, which is 2 inches, with the last loose lift left 1 to 1.5 cm above pavement level so it settles flush when compacted.
Against that 2-inch figure, fixture A at 2.75 inches average depth needs 2 lifts, and fixture B at 3 inches average depth also needs 2 lifts. The lift count uses the average depth, while the maximum depth warns the crew where the first lift will run thickest. Agency practice differs: a Missouri DOT repair revision sets lifts at not greater than 3 inches. That difference is exactly why the label of the product bought, not a single number from this page, controls the lift plan.
Caltrans also calls for a tack coat of asphalt emulsion on the sides and bottom of a semi-permanent patch, at about 0.2 gallon per square yard, sprayed or brushed on, never poured. Tack area comes from the same squared measurements: side area is perimeter times depth, and bottom area is the patch area already recorded.
What this measurement does not decide
The volume figure answers one question: how big is the squared hole. Product choice and bag count each need their own check against a product label and a supplier quote, and neither figure appears on this page. Loose versus compacted thickness is a separate question, covered by the companion thickness guide, because the hole volume and the delivered loose volume are different states of the same material.
Base condition is the limit that matters most. A patch over firm, dry base is a measurement job. A patch over soft, pumping, or alligatored ground signals a base problem, and filling the hole does not repair the base. Record the condition honestly on the measurement sheet so the repair decision is made with the evidence visible, not after the hole is already filled.
Common measurement mistakes
- Measuring the ragged pothole outline instead of the squared patch.
- Taking one depth reading at the centre and missing deep pockets and shallow shelves.
- Mixing inches and feet inside one patch without converting.
- Drawing one bounding rectangle around an irregular patch and overstating its area.
- Using the maximum depth for volume and overstating the hole.
- Recording only the average depth and losing the lift plan for the deep pocket.
- Measuring through loose debris, water, or rubble instead of to the firm base.
- Combining several holes into one figure instead of one row per patch.
Sources and scope
- Caltrans, Maintenance Technical Advisory Guide, Volume I, Chapter 5, Patching and Edge Repair (October 2007): rectangular boundaries slightly larger than the distress, square cut, sides to sound pavement, patch depth 50 percent thicker than the failed layer, tack coat about 0.2 gal/yd2 sprayed or brushed. Accessed 2026-10-27.
- Pavement Interactive, HMA Patching, summarising FHWA (June 1998): semi-permanent steps, vertical sides, intact pavement on all sides, centre mound tapering to flush edges, compact centre outward, slight crown. Accessed 2026-10-27.
- FHWA, Long-Term Monitoring of Pavement Maintenance Materials Test Sites, FHWA-RD-98-073 (June 1998): semi-permanent patching procedure. Accessed 2026-10-27.
- PRO-ROAD, Cold Mix application instructions: lifts maximum 5 cm (2 in), compact each lift, last loose lift 1 to 1.5 cm above level, compact edges toward centre. Accessed 2026-10-27.
- Engineer Fix, How to Calculate How Much Cold Patch You Need: several depth readings because depth varies most, average or maximum as reference depth, 2-inch lift guidance. Accessed 2026-10-27.
- NIST Handbook 44, 2026, Appendix C: the conversion relationships used for the worked examples. Accessed 2026-10-27.
Scope: the figures on this page describe how to measure one squared asphalt patch and calculate its hole volume. They do not set a universal lift thickness, bag count, tonnage, price, or repair method. The governing product label, project specification, site condition, and responsible qualified people control the purchase and the repair for a real pavement.
Review responsibility: Saleem Sial owns the published calculation and editorial checks. The source list above is part of that check. Waseem Sial, External Reviewer and Engineer, remains listed for ongoing external review; no completed external-review date is claimed.
For the thickness question, use the loose versus compacted thickness guide. For a sealed-surface area, use the asphalt sealcoat measurement guide, or return to the Asphalt Calculators hub.
