Unit Conversions for Machining — Metric, Imperial, Pressure, Flow, Power Reference

Complete unit conversion reference for machining engineers. Common conversions for length, pressure, flow, power, torque, temperature, and speed used in deep hole drilling.

Deep Hole DrillingReference5 min read

Length

Convert From To Multiply By
mm → in 1 mm inch 0.03937
in → mm 1 in mm 25.4
m → ft 1 m ft 3.281
ft → m 1 ft m 0.3048
µm → in 1 µm inch 0.00003937
in → µm 1 in µm 25,400

Speed

Convert From To Multiply By
m/min → SFM 1 m/min SFM 3.281
SFM → m/min 1 SFM m/min 0.3048
mm/min → in/min 1 mm/min IPM 0.03937
in/min → mm/min 1 IPM mm/min 25.4
mm/rev → in/rev 1 mm/rev IPR 0.03937
in/rev → mm/rev 1 IPR mm/rev 25.4

Pressure

Convert From To Multiply By
bar → psi 1 bar psi 14.504
psi → bar 1 psi bar 0.06895
MPa → psi 1 MPa psi 145.04
psi → MPa 1 psi MPa 0.006895
bar → MPa 1 bar MPa 0.1
MPa → bar 1 MPa bar 10
atm → bar 1 atm bar 1.013
bar → atm 1 bar atm 0.987

Flow Rate

Convert From To Multiply By
L/min → GPM 1 L/min GPM 0.2642
GPM → L/min 1 GPM L/min 3.785
m³/h → L/min 1 m³/h L/min 16.67
L/min → m³/h 1 L/min m³/h 0.06

Power

Convert From To Multiply By
kW → hp 1 kW hp 1.341
hp → kW 1 hp kW 0.7457
W → hp 1 W hp 0.00134
hp → W 1 hp W 745.7

Torque

Convert From To Multiply By
N·m → ft·lb 1 N·m ft·lb 0.7376
ft·lb → N·m 1 ft·lb N·m 1.356
N·m → in·lb 1 N·m in·lb 8.851
in·lb → N·m 1 in·lb N·m 0.113
kgf·m → N·m 1 kgf·m N·m 9.807

Temperature

Convert Formula
°C → °F (°C × 9/5) + 32
°F → °C (°F − 32) × 5/9
K → °C K − 273.15

Common values: 20°C = 68°F (shop temp), 100°C = 212°F (boiling water), 850°C = 1,562°F (TiAlN coating limit).

Force

Convert From To Multiply By
N → lbf 1 N lbf 0.2248
lbf → N 1 lbf N 4.448
kN → lbf 1 kN lbf 224.8
kgf → N 1 kgf N 9.807

Area / Volume

Convert From To Multiply By
mm² → in² 1 mm² in² 0.00155
in² → mm² 1 in² mm² 645.2
cm³ → in³ 1 cm³ in³ 0.06102
in³ → cm³ 1 in³ cm³ 16.39
L → gal (US) 1 L gal 0.2642
gal (US) → L 1 gal L 3.785

Drill Diameter — Fractional / Decimal / mm

Fraction (in) Decimal (in) mm Nearest mm drill
1/16 0.0625 1.59 1.5
3/32 0.0938 2.38 2.4
1/8 0.125 3.18 3.2
5/32 0.156 3.97 4.0
3/16 0.188 4.76 4.8
1/4 0.250 6.35 6.4
5/16 0.313 7.94 8.0
3/8 0.375 9.53 9.5
7/16 0.438 11.11 11.0
1/2 0.500 12.70 12.7
5/8 0.625 15.88 16.0
3/4 0.750 19.05 19.0
7/8 0.875 22.23 22.2
1 1.000 25.40 25.4
1-1/4 1.250 31.75 32.0
1-1/2 1.500 38.10 38.0
1-3/4 1.750 44.45 44.5
2 2.000 50.80 51.0

Common Coolant Conversions

bar psi MPa Notes
10 145 1.0 Minimum for conventional coolant
40 580 4.0 Minimum for gun drilling on CNC
70 1,015 7.0 Recommended for Inconel (1000 psi)
100 1,450 10.0 BTA production standard
150 2,175 15.0 Small-diameter gun drilling
200 2,900 20.0 High-pressure systems
Threshold 100 psi 6.9 bar Skin puncture hazard

Source: Standard engineering conversion factors; UNISIG; ISCAR; Guhring.

Deep Hole Drilling Editorial Team

We provide independent, practical content for deep hole drilling and precision manufacturing professionals. Our articles are researched and reviewed to ensure technical accuracy and relevance.

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