kg/m³ to lb/ft³ Converter
1 kg/m³ = 0.06242796 lb/ft³. The exact factor comes from: 1 kg = 2.20462262184878 lb (by the exact definition 1 lb = 0.45359237 kg), and 1 m³ = 35.3146667214886 ft³ (since 1 m =...
Formula
Source: NIST SP 811, ISO 80000-4 | Last reviewed: June 27, 2026
Examples
1 kg/m³
= 0.0624 lb/ft³
1 kg/m³ = 0.0624 lb/ft³
1000 kg/m³
= 62.43 lb/ft³
Density of water at 4°C
1.225 kg/m³
= 0.0765 lb/ft³
Density of air at sea level, 15°C
998 kg/m³
= 62.3 lb/ft³
Density of water at 20°C (room temperature)
1025 kg/m³
= 63.99 lb/ft³
Density of seawater (3.5% salinity at 20°C)
Quick Reference Table
| Material | kg/m³ | lb/ft³ |
|---|---|---|
| Air (15°C, 1 atm) | 1.225 | 0.0765 |
| Water (4°C, max density) | 1000 | 62.43 |
| Water (20°C) | 998 | 62.31 |
| Seawater (20°C, 3.5% salt) | 1025 | 63.99 |
| Gasoline | 720-780 | 44.9-48.7 |
| Diesel fuel | 830-870 | 51.8-54.3 |
| SAE 30 motor oil | 875 | 54.6 |
| Crude oil (light, 35° API) | 850 | 53 |
| Crude oil (heavy, 20° API) | 933 | 58.2 |
| Glycerin | 1260 | 78.6 |
| Sulfuric acid (98%) | 1840 | 114.8 |
| Concrete (normal weight) | 2400 | 150 |
| Carbon steel | 7850 | 490 |
| Stainless steel (304) | 8000 | 499 |
| Aluminum | 2700 | 168.5 |
| Copper | 8960 | 559 |
| Lead | 11340 | 707 |
| Mercury | 13560 | 846 |
| Gold | 19320 | 1206 |
| Natural gas (0°C, 1 atm) | 0.717 | 0.0448 |
| Propane (0°C, 1 atm) | 1.88 | 0.1174 |
Where is this used?
The exact factor comes from: 1 kg = 2.20462262184878 lb (by the exact definition 1 lb = 0.45359237 kg), and 1 m³ = 35.3146667214886 ft³ (since 1 m = 3.28083989501312 ft, cubed).
Therefore 1 kg/m³ = 2.20462 / 35.3147 = 0.06242796 lb/ft³.
The density of water at 4°C (maximum density) is 1,000 kg/m³ = 62.428 lb/ft³, and this equivalence — 1,000 ↔ 62.4 — is worth memorizing as a sanity check.
The kg/m³ to lb/ft³ conversion is the fundamental density bridge between the SI and US customary systems.
Every fluid mechanics calculation that involves density — the Reynolds number (Re = ρVD/μ), the Bernoulli equation (P/ρ + V²/2 + gz = constant), buoyancy forces (F = ρgV), pump power (WHP = Q·ΔP/1714, where density is embedded in ΔP for head-based calculations), and pipe friction factor (Darcy-Weisbach: h_f = f·L/D·V²/2g) — requires consistent density units.
A European pump manufacturer (Grundfos, KSB, Sulzer) provides pump performance curves in meters of head and power in kW, with fluid properties in kg/m³.
The US engineer integrating this pump into a system designed in feet and horsepower must convert the fluid density from kg/m³ to lb/ft³ to verify the pump's NPSH (Net Positive Suction Head) and power requirements against the US system hydraulics.
A typical application: a US water treatment plant specifying a pump for a process fluid with SG = 1.05 (density = 1,050 kg/m³).
The US pump supplier needs the density in lb/ft³: 1,050 × 0.06243 = 65.55 lb/ft³.
The pump's required horsepower is directly proportional to density: a 10% error in density conversion (e.g., using 62.4 instead of 65.55) produces a 10% error in HP requirements, potentially undersizing the motor.
For natural gas density calculations at standard conditions (0°C and 1 atm), methane has a density of approximately 0.717 kg/m³ = 0.0448 lb/ft³.
At pipeline pressures of 1,000 psig, natural gas density rises to approximately 50-80 kg/m³ (3-5 lb/ft³), which is still far less than liquid densities but approaches them — and the density determines the pipeline's mass flow capacity.
In combustion engineering, the air-fuel ratio calculations require both air density and fuel density: air at standard conditions is 1.225 kg/m³ = 0.0765 lb/ft³, and converting between these is essential when the combustion air blower is sized in ACFM (actual cubic feet per minute) based on local air density and the international fuel specification is in kg/h.
A 5 MW gas turbine consuming 0.3 kg/s of natural gas (about 1,080 kg/h) with an air-fuel ratio of 50:1 by mass draws 15 kg/s of air (54,000 kg/h).
At sea-level air density of 1.225 kg/m³, this is 15 / 1.225 = 12.24 m³/s (25,930 ACFM).
The US engineer converting to ACFM uses lb/ft³ density: air flow = 15 kg/s × 2.2046 lb/kg = 33.07 lb/s, ÷ 0.0765 lb/ft³ = 432.3 ft³/s = 25,940 ACFM — matching the SI calculation.
The kg/m³ to lb/ft³ conversion is one of the most reliable in engineering because the mass-length conversion factors are exact by international agreement.
Real-World Usage Scenarios
European pump integration in US water treatment plant
A US municipal water treatment plant is upgrading its coagulation chemical feed system, replacing centrifugal pumps that have reached end of service life. The new pumps are from a European manufacturer (Grundfos, KSB, or Sulzer), specified in metric units: flow 50 m³/h, head 20 m, fluid density 1,100 kg/m³ (a ferric chloride solution at 10% concentration). The US engineer converting to US customary units for the plant's hydraulic calculation: flow 50 m³/h × 4.403 = 220 GPM; head 20 m × 3.281 = 65.6 ft; density 1,100 × 0.06243 = 68.67 lb/ft³. The pump brake horsepower (BHP) calculation: WHP = (Q × H × SG) / 3,960 = (220 × 65.6 × 1.1) / 3,960 = 4.0 HP. With 75% pump efficiency: BHP = 4.0 / 0.75 = 5.34 HP — select a 7.5 HP motor with service factor. The kg/m³ to lb/ft³ conversion (× 0.06243) is applied to the fluid density, and the horsepower calculation uses the US customary formula with the converted density. A 1% error in the density conversion (using 62.43 lb/ft³ instead of 68.67) would understate the horsepower by about 10%, undersizing the motor and causing it to trip on overload.
Industry Standards Referenced
Frequently Asked Questions
How accurate is the 0.06243 conversion factor?
The exact factor is 0.062427960576, derived from the exact definitions of kg (→ lb: 1/0.45359237 = 2.204622622) and m (→ ft: 1/0.3048 = 3.280839895), cubed to get m³ → ft³: 35.314666721. The ratio yields 0.0624279606. The commonly used 0.06243 has 4 significant figures and a 0.003% error — negligible for almost all industrial fluid density calculations. Water density at 1,000 kg/m³ converts to 62.428 lb/ft³ using the exact factor, versus 62.43 using the rounded factor — a 0.003% difference.
Why does European data use kg/m³ while US uses lb/ft³?
SI (metric) adoption in Europe vs continued use of US customary (foot-pound-second) system. European pipe sizing (DN, in mm), pump curves (meters head, kW power), and fluid properties (kg/m³, Pa·s viscosity) are natively SI. US pipe sizing (NPS, in inches), pump curves (feet head, HP), and fluid properties (lb/ft³, cP or lb/ft·s viscosity) use US customary. The kg/m³-to-lb/ft³ conversion bridges these two universes for any equipment or process that crosses the Atlantic.
How do I convert kg/m³ to specific gravity (SG)?
SG is dimensionless and equals the density divided by the density of water at the reference temperature. SG = ρ(kg/m³) / 1000 (at 4°C, the standard SG reference). SG = ρ(lb/ft³) / 62.428 (at 4°C). A fluid with density 1,050 kg/m³ has SG = 1.05. Note: SG is sometimes defined at 60°F (15.6°C) instead of 4°C for petroleum measurements (API) — at 60°F, water density is 999.04 kg/m³, so SG(60°F) = ρ / 999.04. The difference is small (0.1%) but matters for precise petroleum custody transfer calculations.
Reviewed for accuracy
Verified against NIST and ISO standard mass and length conversions · Last reviewed: June 27, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.