What is the unit weight of concrete?

Plain normalweight concrete is customarily taken as 145 pcf (22.8 kN/m³) and reinforced concrete as 150 pcf (23.6 kN/m³) — the extra 5 pcf covers typical reinforcement. Lightweight structural concrete runs roughly 90–115 pcf. These are the ASCE 7 dead-load convention values.

What is the unit weight of water?

Fresh water: 62.4 pcf (9.81 kN/m³) at ordinary temperatures. Seawater: about 64.0 pcf (10.05 kN/m³). These anchor hydrostatic pressure (p = γ·h), buoyancy, and uplift calculations — a 10-ft water column exerts 624 psf.

What unit weight should I use for soil?

Moist compacted structural fill is commonly 110–130 pcf; loose dry sand 90–110; saturated sand 115–135; soft clay 100–120; stiff clay 115–135. For design, use lab or field data (nuclear gauge, drive cylinder) whenever available — soil unit weight varies enough to matter in earth-pressure and settlement results. The values here are screening ranges.

Why do gabion and riprap weights differ from solid rock?

Solid rock (granite, limestone) weighs about 160–170 pcf, but dumped or basket-placed stone contains 30–40% voids, so the bulk assembly weighs roughly 100–120 pcf. Use the solid unit weight for sizing individual stones against hydraulic forces, and the bulk unit weight for gravity-mass calculations like gabion wall stability.

Are these values suitable for final design?

They are standard handbook values (ASCE 7 Table C3.1-1a and geotechnical references) appropriate for preliminary sizing and checking. For final structural design use the project's actual materials, and for soils use the geotechnical report. Where a range is shown, the conservative end depends on whether the load helps or hurts — heavier is conservative for demand, lighter for resisting mass.

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Unit Weights of Construction Materials — Reference

By Michael Flynn, PE · water resources & dam safety engineer · Last updated Oct 18, 2026

Dead-load and geotechnical unit weights in US customary (pcf) and SI (kN/m³). Conversion: 1 pcf = 0.1571 kN/m³.

Water & Fluids

Material	pcf	kN/m³
Fresh water	62.4	9.81
Seawater	64.0	10.05
Ice	57	9.0

Structural Materials

Material	pcf	kN/m³
Concrete, plain (normalweight)	145	22.8
Concrete, reinforced	150	23.6
Concrete, structural lightweight	90–115	14–18
Steel	490	77.0
Aluminum	165–170	26–27
Timber, softwood (SYP, DF)	32–37	5.0–5.8
Timber, hardwood	40–47	6.3–7.4
Brick masonry	120–130	19–20
CMU, grouted solid (normalweight)	135–140	21–22
Asphalt pavement (HMA)	140–145	22–23
Glass	160	25.1

Soils & Aggregates (moist unless noted)

Material	pcf	kN/m³
Sand, loose, dry	90–110	14–17
Sand, compacted	110–130	17–20
Sand, saturated	115–135	18–21
Clay, soft	100–120	16–19
Clay, stiff	115–135	18–21
Silt	100–125	16–20
Gravel / sandy gravel, compacted	120–140	19–22
Crushed stone base (compacted)	125–145	20–23
Structural fill (typ. design value)	120	18.9
Rock, solid (granite, limestone)	160–170	25–27
Riprap / gabion stone, bulk (30–40% voids)	100–120	16–19
Topsoil	80–100	13–16

Buoyant unit weight.

γ′ = γ_sat − γ_w

Below the water table, effective (buoyant) unit weight drives effective stress: saturated sand at 125 pcf has γ′ = 125 − 62.4 ≈ 63 pcf — half the total. Using total instead of buoyant weight below the water table is one of the classic geotechnical calculation errors.

Sources: ASCE/SEI 7-22, Table C3.1-1a (materials). Das, B.M., Principles of Geotechnical Engineering (soils). Terzaghi & Peck, Soil Mechanics in Engineering Practice. Ranges are handbook screening values; project-specific data governs final design.

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Worked example: effective stress with a water table

Vertical stress at 15 ft depth, water table at 5 ft, sand profile

Given moist sand γ = 115 pcf above the water table, saturated sand γ_sat = 125 pcf below, γ_w = 62.4 pcf

Find total stress, pore pressure, effective stress at 15 ft

Total stress σ = 5 × 115 + 10 × 125 = 575 + 1,250 = 1,825 psf

Pore pressure u = 10 ft of water × 62.4 = 624 psf

Effective stress σ′ = 1,825 − 624 = 1,201 psf

Same answer the buoyant way: 5 × 115 + 10 × (125 − 62.4) = 575 + 626 = 1,201 psf

Using the total stress instead of the effective stress overstates the stress that controls friction, bearing and settlement by 52% at this depth. Effective stress is what sets sliding resistance on a retaining wall base, skin friction on a pile and the consolidation load on a clay layer. The total-stress number looks reasonable on paper, which is why this mistake gets past review.

Common mistakes

Using the moist unit weight below the water table. Below the water table, saturated weight goes into total stress and buoyant weight goes into effective stress. Moist weight is wrong for both.
Taking a single “120 pcf” for everything. Structural fill at 120 pcf is a design convention, not a measured value. Riprap at 100–120 pcf bulk is lighter than the 160–170 pcf of the rock it is made of, because 30–40% of its volume is voids.
Using reinforced-concrete weight for uplift resistance at 150 pcf when the section is mostly plain concrete. For uplift and flotation checks, the lower value and a factor of safety are the conservative choice.
Forgetting that a rising water table makes an earlier calculation wrong. A design groundwater level below the seasonal high gives effective stresses that are not there in a wet spring.

When this card doesn’t apply

These are screening ranges from handbooks and ASCE 7 commentary. A geotechnical report’s measured unit weights replace them as soon as one exists. Organic soils, peat, collapsible loess and fills with debris fall outside these ranges and need laboratory values. For dead loads in structural design, ASCE/SEI 7 Table C3.1-1a and the manufacturer’s published weights for specific products govern.

Related cheat sheets and tools

Pair with the presumptive bearing values card for foundation screening, the exit gradient tool for buoyant-weight seepage checks, and the gravity dam stability tool where mass is the resistance.