MPa · kN · kN/m² · mm · Tonnes · PSI · Bar · Feet · Inches – Instant Engineering Converters
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1 MPa = 145.038 PSI | 1 PSI = 0.006895 MPa
Common values: Concrete C30/37 = 30 MPa cylinder = 4,351 PSI
1 MPa = 1,000 kN/m² = 1,000 kPa | 1 kN/m² = 0.001 MPa
EC2: Steel yield fy = 275 N/mm² = 275,000 kN/m²
1 N/mm² = 10.197 kgf/cm² | Used in older BS / IS codes
1 bar = 14.504 PSI | 1 PSI = 0.06895 bar
Note: 1 bar ≈ 100 kPa ≈ 0.987 atm; water pressure at 10m depth ≈ 1 bar
| Value | MPa (N/mm²) | kN/m² | PSI | Bar | kgf/cm² |
|---|---|---|---|---|---|
| Concrete C20/25 (fck cube) | 25 | 25,000 | 3,626 | 250 | 255 |
| Concrete C30/37 (fck cube) | 37 | 37,000 | 5,366 | 370 | 377 |
| Concrete C40/50 (fck cube) | 50 | 50,000 | 7,252 | 500 | 510 |
| Steel S275 yield (fy) | 275 | 275,000 | 39,885 | 2,750 | 2,804 |
| Steel S355 yield (fy) | 355 | 355,000 | 51,488 | 3,550 | 3,620 |
| Steel S275 ultimate (fu) | 430 | 430,000 | 62,366 | 4,300 | 4,385 |
| Rebar B500B yield (fyk) | 500 | 500,000 | 72,519 | 5,000 | 5,099 |
| Atmospheric pressure | 0.101325 | 101.325 | 14.696 | 1.013 | 1.033 |
| Water at 10m depth | 0.098 | 98 | 14.22 | 0.98 | 1.0 |
| Tyre pressure (typical car) | 0.207–0.241 | 207–241 | 30–35 | 2.07–2.41 | 2.11–2.46 |
| Modulus of elasticity – Steel (E) | 210,000 | 210,000,000 | 30,458,000 | 2,100,000 | 2,141,000 |
| Modulus of elasticity – Concrete C30 | ~33,000 | 33,000,000 | 4,786,000 | 330,000 | 336,600 |
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1 tf = 9.807 kN | 1 kN = 0.1020 tf ≈ 102 kgf
Uniformly distributed load | 1 kN/m = 101.97 kgf/m
1 kN/m² = 101.97 kgf/m² | 1 kgf/m² = 0.00981 kN/m²
1 kN = 224.809 lbf = 0.2248 kip (1 kip = 1,000 lbf = 4.448 kN)
| Value / Context | kN | N | kgf (approx.) | lbf | Notes |
|---|---|---|---|---|---|
| Weight of 1 tonne mass | 9.807 | 9,807 | 1,000 | 2,205 | g = 9.807 m/s² |
| Domestic floor imposed load (1.5 kN/m²) on 3m×5m | 22.5 kN | 22,500 | 2,294 | 5,059 | EC1 Cat A residential |
| Point load from 100kg person | 0.981 | 981 | 100 | 220 | — |
| Self-weight of 203×133×25 UB per metre | 0.246 | 246 | 25.1 | 55 | 25.1 kg/m × 9.807 |
| Self-weight RC slab 150mm on 1m² plan | 3.75 | 3,750 | 383 | 843 | 25 kN/m³ × 0.15m |
| Wind pressure on wall (0.8 kN/m²) on 10m² | 8.0 | 8,000 | 816 | 1,798 | — |
| Typical 2-storey house column reaction | 100–400 | — | 10,000–40,000 | 22,480–89,924 | Depends on loading bay |
1 inch = 25.4 mm exactly | 1 mm = 0.03937 in
1 ft = 0.3048 m | 1 m = 3 ft 3.37 in
Most commonly used length units in UK structural engineering
Second moment of area | 1 cm⁴ = 10,000 mm⁴ = 0.02403 in⁴
| mm | cm | m | inches | feet | Common context |
|---|---|---|---|---|---|
| 1 | 0.1 | 0.001 | 0.03937 | 0.003281 | Rebar cover tolerance, tile grout |
| 10 | 1.0 | 0.010 | 0.3937 | 0.03281 | Mortar joint, cover tolerance Δcdev |
| 25 | 2.5 | 0.025 | 0.984 | 0.0820 | Concrete cover – XC1 (1 inch) |
| 25.4 | 2.54 | 0.0254 | 1.000 | 0.0833 | Exactly 1 inch |
| 40 | 4.0 | 0.040 | 1.575 | 0.1312 | Concrete cover – XC4 external |
| 100 | 10.0 | 0.100 | 3.937 | 0.3281 | Min slab thickness, insulation depth |
| 150 | 15.0 | 0.150 | 5.906 | 0.4921 | Standard RC slab thickness |
| 305 | 30.5 | 0.305 | 12.00 | 1.000 | Exactly 1 foot (304.8mm rounded) |
| 914 | 91.4 | 0.914 | 36.00 | 3.000 | 1 yard |
| 1,000 | 100.0 | 1.000 | 39.37 | 3.281 | 1 metre |
| 3,048 | 304.8 | 3.048 | 120.0 | 10.00 | 10 feet |
| m² | cm² | mm² | ft² | in² | Context |
|---|---|---|---|---|---|
| 0.000113 | 1.131 | 113.1 | 0.00122 | 0.1754 | T12 rebar cross-section area (1 bar) |
| 0.000201 | 2.011 | 201.1 | 0.00216 | 0.3117 | T16 rebar cross-section area (1 bar) |
| 0.000393 | 3.927 | 392.7 | 0.00423 | 0.6090 | A393 mesh (393 mm²/m per metre width) |
| 1.0 | 10,000 | 1,000,000 | 10.764 | 1,550 | 1 square metre |
| 9.29 | 92,903 | 9,290,304 | 100 | 14,400 | 100 sq ft |
| 20 | 200,000 | 20,000,000 | 215.3 | 31,000 | Typical medium extension footprint |
| m³ | litres | ft³ | yd³ | Context |
|---|---|---|---|---|
| 0.090 | 90 | 3.18 | 0.118 | One 130L drum mixer load (usable output) |
| 0.5 | 500 | 17.66 | 0.654 | Approx. volume of one bulk aggregate bag |
| 1.0 | 1,000 | 35.31 | 1.308 | 1 m³ – standard concrete ordering unit |
| 4.0 | 4,000 | 141.3 | 5.232 | Typical ready-mix minimum load |
| 6.0 | 6,000 | 211.9 | 7.848 | Full ready-mix truck load (UK, 6–8 m³) |
| 7.0 | 7,000 | 247.2 | 9.153 | Max ready-mix load (most UK trucks) |
| kg | tonnes | lbs | Context |
|---|---|---|---|
| 25 | 0.025 | 55.1 | Standard bag (cement, sand, aggregate, mortar) |
| 850 | 0.85 | 1,874 | Standard UK bulk bag (jumbo / tonne bag – nominal) |
| 1,000 | 1.0 | 2,205 | 1 tonne – standard UK aggregate ordering unit |
| 2,500 | 2.5 | 5,512 | Self-weight of 1 m³ reinforced concrete |
| 7,850 | 7.85 | 17,306 | Self-weight of 1 m³ structural steel |
| 20,000 | 20.0 | 44,092 | Max payload – standard 4-axle tipper truck (UK) |
| 30,000 | 30.0 | 66,139 | Max payload – artic tipper (UK road weight) |
| Material | kg/m³ | kN/m³ | g/cm³ | lb/ft³ |
|---|---|---|---|---|
| Reinforced concrete | 2,500 | 24.5 | 2.50 | 156 |
| Plain concrete (unreinforced) | 2,300 | 22.6 | 2.30 | 144 |
| Aerated concrete block (AAC) | 600 | 5.9 | 0.60 | 37 |
| Structural steel | 7,850 | 77.0 | 7.85 | 490 |
| Aluminium (structural alloy) | 2,700 | 26.5 | 2.70 | 169 |
| Softwood timber (dry, C24) | 420 | 4.1 | 0.42 | 26 |
| Hardwood timber (dry, oak) | 750 | 7.4 | 0.75 | 47 |
| Clay brick (facing) | 1,900 | 18.6 | 1.90 | 119 |
| Clay brick (engineering) | 2,100 | 20.6 | 2.10 | 131 |
| Sand (dry, loose) | 1,500 | 14.7 | 1.50 | 94 |
| Gravel / shingle (loose) | 1,600 | 15.7 | 1.60 | 100 |
| MOT Type 1 (compacted) | 2,100 | 20.6 | 2.10 | 131 |
| Water (at 4°C) | 1,000 | 9.81 | 1.00 | 62.4 |
| Seawater | 1,025 | 10.05 | 1.025 | 64 |
| Scenario | kN·m | N·mm | kgf·m | ft·lbf |
|---|---|---|---|---|
| Simply supported beam – UDL: M = wL²/8 | e.g. w=10kN/m, L=5m → M = 31.25 kN·m | |||
| w=10 kN/m, L=5m (wL²/8) | 31.25 | 31,250,000 | 3,186 | 23,043 |
| w=20 kN/m, L=6m (wL²/8) | 90.0 | 90,000,000 | 9,174 | 66,371 |
| Cantilever – UDL: M = wL²/2 | e.g. w=5kN/m, L=2m → M = 10 kN·m | |||
| P=100kN at mid-span of 5m SS beam (PL/4) | 125 | 125,000,000 | 12,742 | 92,173 |
| Elastic section modulus – 203×133×25 UB (Zx) | Zx = 231 cm³ = 231,000 mm³; capacity at S275: M = 275 × 231,000 / 10⁶ = 63.5 kN·m | |||
R = 1/U | U = 1/R | Higher R = better insulation; Lower U = better insulation
R = thickness(m) / λ | e.g. 100mm PIR (λ=0.023): R = 0.1/0.023 = 4.35 m²K/W
Imperial thermal conductivity unit | 1 W/mK = 6.933 BTU·in/(h·ft²·°F)
| Material / Element | λ (W/mK) | Thickness | R (m²K/W) | U (W/m²K) |
|---|---|---|---|---|
| PIR board insulation | 0.023 | 100mm | 4.35 | 0.23 |
| PIR board insulation | 0.023 | 150mm | 6.52 | 0.15 |
| EPS expanded polystyrene | 0.036 | 100mm | 2.78 | 0.36 |
| Mineral wool quilt | 0.038 | 200mm | 5.26 | 0.19 |
| Mineral wool quilt | 0.038 | 270mm (loft) | 7.11 | 0.14 |
| Cavity wall (full-fill mineral wool) | 0.036 | 100mm cavity | 2.78 | — |
| Dense concrete | 2.00 | 200mm | 0.10 | — |
| Brick (facing) | 0.77 | 102.5mm | 0.133 | — |
| Plasterboard | 0.21 | 12.5mm | 0.060 | — |
| Internal surface resistance Rsi (wall) | — | — | 0.13 | — |
| External surface resistance Rse | — | — | 0.04 | — |
| Description | Degrees | % Gradient | 1 in N | Radians |
|---|---|---|---|---|
| Minimum drainage fall (flat roof) | 1.1° | 2% | 1:50 | 0.020 |
| Min. fall BS 5534 pitched roof to gutter | 0.6° | 1% | 1:100 | 0.010 |
| Minimum pitched roof – concrete tiles (BS 5534) | 15° | 26.8% | 1:3.73 | 0.262 |
| Typical domestic pitched roof (30°) | 30° | 57.7% | 1:1.73 | 0.524 |
| Minimum slate – natural (BS 5534) | 20° | 36.4% | 1:2.75 | 0.349 |
| Maximum stair pitch (Building Regs Part K) | 42° | 90.0% | 1:1.11 | 0.733 |
| Ramp gradient – wheelchair accessible (Part M) | 3.4° | 6% | 1:16.7 | 0.059 |
| Ramp gradient – general (Part K) | 5.7° | 10% | 1:10 | 0.100 |
| Road camber (typical UK) | 1.1–2.3° | 2–4% | 1:25–1:50 | — |
| 45° (equal rise and run) | 45° | 100% | 1:1 | 0.785 |
| Angle of repose – dry sand | ~34° | ~67% | ~1:1.48 | 0.593 |
| Angle of repose – clay | ~15–35° | 26–70% | 1:1.4–1:3.7 | — |
UK construction and structural engineering uses SI (Système International) units as the primary system, following the adoption of Eurocodes and BS EN standards. However, engineers regularly encounter non-SI units in older British Standards, American references, material datasheets, and contractor-supplied data — making unit conversion an everyday requirement in UK construction practice in 2026.
The most frequently converted units in UK structural and civil engineering are: stress and pressure (MPa / N/mm² to PSI and kgf/cm²); force and load (kN to tonnes-force and lbf); length (mm to inches and feet); and bending moment (kN·m to kgf·m and ft·lbf). The converters above cover all of these and more, with quick-reference tables of common engineering values in each unit system.
1 MPa = 1 N/mm² exactly. This is because 1 Pa = 1 N/m², and 1 m² = 10⁶ mm², so 1 MPa = 10⁶ N/m² = 1 N/mm². Concrete strength (fck), steel yield strength (fy), and elastic modulus (E) are all expressed in N/mm² (= MPa) in UK Eurocodes. The unit N/mm² is used in most UK structural calculations; MPa is used more often in concrete technology and testing contexts.
1 kN/m² = 1 kPa (kilopascal) exactly, because 1 kN = 1,000 N and 1 m² = 1 m². Imposed floor loads, wind pressures, and soil bearing pressures are all expressed in kN/m² in Eurocode structural design. The soil bearing pressure for a strip foundation, the wind pressure on a cladding panel, and the live load on a floor slab are all in kN/m².
A tonne (t) is a unit of mass (1,000 kg). A tonne-force (tf) is a unit of force equal to the weight of 1 tonne mass under standard gravity (g = 9.80665 m/s²), i.e. 1 tf = 9.807 kN. In everyday construction contexts, "tonnes" is often loosely used to mean "tonnes-force" — important to distinguish when converting to kN for structural calculations.
PSI (pounds per square inch) is an imperial pressure unit not used in UK Eurocode design but still encountered in: US structural references; some material datasheets (adhesives, sealants, gas pressures); hydraulic system specifications; and tyre pressures. 1 MPa = 145.038 PSI. Concrete C30/37 (37 N/mm² cube strength) = 5,366 PSI.
The international inch was defined as exactly 25.4 mm in 1959. This exact relationship simplifies inch-to-metric conversion. Common fractions: ½ in = 12.7mm; ¼ in = 6.35mm; ⅛ in = 3.175mm. Standard rebar cover spacers in the UK are sold in mm increments (20mm, 25mm, 30mm, 40mm, 50mm) — easily converted to approximate inch values for US reference documents.
The thermal transmittance U-value (W/m²K) and the thermal resistance R-value (m²K/W) are reciprocals: R = 1/U and U = 1/R. Lower U-value = better insulation. Higher R-value = better insulation. UK Building Regulations specify limits in U-values (e.g. wall ≤ 0.18 W/m²K). US insulation products are often rated in R-values — important to convert when using US product data in UK designs.
There is no difference — 1 MPa = 1 N/mm² exactly. The megapascal (MPa) and the newton per square millimetre (N/mm²) are numerically identical units of stress and pressure. The Pascal is defined as 1 N/m², so 1 MPa = 10⁶ N/m². Since 1 m² = 10⁶ mm², 1 MPa = 10⁶ N/m² = 1 N/mm². In UK Eurocode structural design, N/mm² is the preferred unit for material strengths (concrete fck, steel fy, timber strength values). MPa is used more often in concrete technology, geotechnical, and international contexts. Both are correct and both appear in UK engineering documentation — understanding they are identical eliminates a very common source of confusion.
To convert kN/m² to MPa, divide by 1,000. This is because: 1 kN/m² = 1 kPa = 0.001 MPa. Conversely, 1 MPa = 1,000 kN/m² = 1,000 kPa. This conversion is used constantly in structural engineering — for example, converting the soil bearing capacity from kN/m² (as reported in a ground investigation) to N/mm² (for checking against foundation contact pressure in N/mm²). A bearing capacity of 150 kN/m² = 0.15 N/mm² = 0.15 MPa.
To convert kN to tonnes-force: divide by 9.807 (since 1 tonne-force = 9.807 kN). To convert tonnes-force to kN: multiply by 9.807. In practice, many UK engineers approximate 10 kN ≈ 1 tonne-force (1.98% error), which is acceptable for quick checks but not for final calculations. A column reaction of 500 kN is approximately 51 tonnes-force (500 / 9.807 = 51.0 tf). Note the distinction between tonne (mass) and tonne-force (force): a mass of 1 tonne exerts a force of 9.807 kN under standard gravity.
Exactly 25.4 mm in 1 inch and exactly 304.8 mm in 1 foot (= 12 × 25.4). These are exact definitions established by international agreement in 1959. Useful practical values: 1 foot = 304.8mm ≈ 305mm; 1 inch = 25.4mm; 6 inches = 152.4mm; 4 inches = 101.6mm (approximately the face dimension of a UK standard brick plus mortar). In the UK, all structural drawings use mm for dimensions — feet and inches appear only in historical drawings, client briefs referencing American standards, or descriptions of US-imported products.
To convert PSI (pounds per square inch) to MPa: divide by 145.038. To convert MPa to PSI: multiply by 145.038. So: 1 PSI = 0.006895 MPa; 1 MPa = 145.038 PSI. Common values: concrete C30/37 (cube strength 37 N/mm²) = 37 × 145.038 = 5,366 PSI; steel S275 yield (fy = 275 N/mm²) = 275 × 145.038 = 39,885 PSI ≈ 40 ksi; tyre pressure 32 PSI = 0.221 MPa = 221 kPa. PSI is not used in UK Eurocode-based structural design but is encountered in US references, hydraulic system specifications, and some material datasheets.
These three units represent different physical quantities used extensively in structural and civil engineering. kN/m is a line load or distributed force per unit length — used for beam self-weight, wall loads on beams, and uniformly distributed loads (UDL) on linear elements (e.g. 15 kN/m on a floor beam). kN/m² is a pressure or area load — used for imposed floor loads, wind pressures, soil pressures, and bearing pressures on foundations (e.g. 1.5 kN/m² domestic floor live load). kN/m³ is a unit weight or force density — used for material self-weights (e.g. concrete 25 kN/m³, steel 78.5 kN/m³, water 9.81 kN/m³). Confusing these three is a common error — always check units carefully in structural calculations.
To convert kN·m to N·mm: multiply by 10⁶ (one million). This is because 1 kN = 1,000 N and 1 m = 1,000 mm, so 1 kN·m = 1,000 N × 1,000 mm = 1,000,000 N·mm = 10⁶ N·mm. This conversion is needed when checking beam bending capacity using elastic section modulus (Zx in cm³, which must be converted to mm³ = cm³ × 1,000) against the design moment in N·mm. For example: M = 50 kN·m = 50 × 10⁶ N·mm; Zx = 231 cm³ = 231,000 mm³; moment capacity = fy × Zx = 275 × 231,000 = 63,525,000 N·mm = 63.5 kN·m.
To convert degrees to percentage gradient: % = tan(degrees) × 100. To convert to 1-in-N ratio: N = 1/tan(degrees). Examples: 30° roof pitch = tan(30°) × 100 = 57.7% gradient = 1 in 1.73. 15° (minimum for concrete tiles) = tan(15°) × 100 = 26.8% = 1 in 3.73. 45° = tan(45°) × 100 = 100% = 1 in 1. In UK roofing, pitch is commonly expressed in degrees (BS 5534); drainage gradients in civil engineering are expressed as a percentage or 1-in-N ratio. The slope / angle converter above does all these conversions automatically.
The U-value (thermal transmittance) measures how quickly heat passes through a building element — lower U-value means better insulation. Units: W/m²K. Used in UK Building Regulations Part L and EC Eurocodes. The R-value (thermal resistance) is the reciprocal of U-value: R = 1/U. Higher R-value means better insulation. Units: m²K/W. R-values are used in North America and appear on many insulation product specifications. To convert: if a product has R-value 4.3 m²K/W, its U-value = 1/4.3 = 0.23 W/m²K. Individual layer R-values (R = thickness/λ) add together to give the total wall R-value, from which the U-value is calculated as U = 1/R_total.
Standards and references for unit conversion in UK construction: BSI Group | Institution of Structural Engineers | Institution of Civil Engineers | The Concrete Society | The Concrete Centre