§ How it works

Every unit on this sheet is defined by how it maps onto one SI base unit for its quantity: watts for power, newton-metres for torque, pascals for pressure, and so on. Converting is a two-step hop through that base.

x_{\text{base}} = x_{\text{from}} \times f_{\text{from}} \qquad\qquad x_{\text{to}} = \frac{x_{\text{base}}}{f_{\text{to}}}

For the units selected now:

1\ \text{kW} = 1.341\ \text{hp}

Temperature is the odd one out

Temperature scales do not share a zero, so they need an offset as well as a factor:

T_{^\circ\text{F}} = T_{^\circ\text{C}} \times \tfrac{9}{5} + 32 \qquad\qquad T_{\text{K}} = T_{^\circ\text{C}} + 273.15

Conversions worth memorising

$1\ \text{hp} = 0.7457\ \text{kW} = 1.0139\ \text{PS}$ . Metric horsepower (PS, CV, cv) is 1.4 % smaller than mechanical hp.
$1\ \text{lb·ft} = 1.3558\ \text{N·m}$ , so 100 lb·ft is about 136 N·m.
$1\ \text{bar} = 14.504\ \text{psi} = 100\ \text{kPa}$ . One bar is very nearly one atmosphere.
$1\ \text{mph} = 1.6093\ \text{km/h}$ . Multiply by 8 and divide by 5 in your head.
$1\ \text{in} = 25.4\ \text{mm}$ exactly, by definition since 1959.
$1\ \text{US gal} = 3.785\ \text{L}$ and $1\ \text{UK gal} = 4.546\ \text{L}$ .

Torque wrench sanity check

A wheel nut torqued to 120 N·m is 88.5 lb·ft. Mixing those up in either direction means a wheel that is 36 % over- or 26 % under-tightened, so it is worth reading the units on the wrench twice.

References

SI Brochure: The International System of Units (SI), 9th ed. — BIPMauthoritative SI definitions
SP 811, Guide for the Use of the International System of Units — NISTUS conversion factors, including 1 in = 25.4 mm exactly

§ How it works

x_{\text{base}} = x_{\text{from}} \times f_{\text{from}} \qquad\qquad x_{\text{to}} = \frac{x_{\text{base}}}{f_{\text{to}}}

For the units selected now:

1\ \text{kW} = 1.341\ \text{hp}

Temperature is the odd one out

Temperature scales do not share a zero, so they need an offset as well as a factor:

T_{^\circ\text{F}} = T_{^\circ\text{C}} \times \tfrac{9}{5} + 32 \qquad\qquad T_{\text{K}} = T_{^\circ\text{C}} + 273.15

Conversions worth memorising

$1\ \text{hp} = 0.7457\ \text{kW} = 1.0139\ \text{PS}$ . Metric horsepower (PS, CV, cv) is 1.4 % smaller than mechanical hp.
$1\ \text{lb·ft} = 1.3558\ \text{N·m}$ , so 100 lb·ft is about 136 N·m.
$1\ \text{bar} = 14.504\ \text{psi} = 100\ \text{kPa}$ . One bar is very nearly one atmosphere.
$1\ \text{mph} = 1.6093\ \text{km/h}$ . Multiply by 8 and divide by 5 in your head.
$1\ \text{in} = 25.4\ \text{mm}$ exactly, by definition since 1959.
$1\ \text{US gal} = 3.785\ \text{L}$ and $1\ \text{UK gal} = 4.546\ \text{L}$ .

Torque wrench sanity check

A wheel nut torqued to 120 N·m is 88.5 lb·ft. Mixing those up in either direction means a wheel that is 36 % over- or 26 % under-tightened, so it is worth reading the units on the wrench twice.

References

SI Brochure: The International System of Units (SI), 9th ed. — BIPMauthoritative SI definitions
SP 811, Guide for the Use of the International System of Units — NISTUS conversion factors, including 1 in = 25.4 mm exactly

Unit Converter

Inputsdrag · tap · type

Fig. 24Slide rule: kW against hp

§ How it works

Temperature is the odd one out

Conversions worth memorising

Torque wrench sanity check

References

Unit Converter

Inputsdrag · tap · type

Fig. 24Slide rule: kW against hp

§ How it works

Temperature is the odd one out

Conversions worth memorising

Torque wrench sanity check

References