长度与距离示例

# Metric Length Basics

Use this quick guide to understand common metric length units:

- 1 millimeter (mm) = thickness of a credit card edge
- 10 millimeters = 1 centimeter (cm)
- 100 centimeters = 1 meter (m)
- 1,000 meters = 1 kilometer (km)

## Everyday references

- A grain of rice is about 6-7 mm long
- A paperclip is about 3 cm long
- A desk is often around 1.2 m wide
- A running track lap is 400 m
- 2.5 laps on a running track is 1 km

## Why this matters

Metric units scale by powers of 10, so they are easy to compare:

- small object -> mm
- hand-sized object -> cm
- room or person -> m
- road or travel distance -> km

## Quick memory rule

mm -> cm -> m -> km
Each step moves by 10, 100, or 1,000 depending on direction.

# Everyday Distance Guide

Distance makes more sense when tied to familiar activities.

## Short distances

- 5 m: about the width of a small bedroom
- 10 m: a short classroom walk
- 100 m: one straight sprint on a track

## Neighborhood scale

- 500 m: a 5-7 minute walk for many people
- 1 km: about a 10-15 minute walk
- 3 km: a short bike ride or commute inside a neighborhood

## City scale

- 5 km: common running distance, short taxi trip
- 10 km: a moderate urban drive
- 20 km: distance between many city districts

## Regional scale

- 50 km: a nearby town
- 100 km: a day trip by car
- 300 km: intercity travel

## Intuition tips

- Walking is often 4 to 6 km/h
- City driving may average 20 to 40 km/h in traffic
- Highway travel often feels much shorter because speed changes your sense of distance

Distance is not just a number. Pair it with travel method and time to make it meaningful.

# Metric and Imperial Reference Sheet

Use this sheet when reading measurements from different countries.

## Small length conversions

- 1 inch = 2.54 cm
- 12 inches = 1 foot
- 1 foot = 30.48 cm
- 3 feet = 0.9144 m

## Medium length conversions

- 1 yard = 0.9144 m
- 1 meter = 3.28084 feet
- 2 meters = about 6 feet 6.7 inches

## Long distance conversions

- 1 mile = 1.609344 km
- 5 miles = 8.04672 km
- 10 km = 6.21371 miles
- Marathon distance: 42.195 km = 26.219 miles

## How to choose units

- inches / centimeters: screens, tools, stationery
- feet / meters: people, furniture, room dimensions
- miles / kilometers: roads, routes, running events

## Common misconceptions

- MB and MiB are different in storage; likewise, miles and kilometers are not close enough to estimate casually in formal work
- 1 mile is not "about 1.5 km" in technical documents; use the exact factor when precision matters
- Feet are useful for height and building dimensions, but meters are easier for scientific or international comparison

## Best practice

If the audience is international, show both units:

- Height: 180 cm (5 ft 10.9 in)
- Distance: 10 km (6.21 mi)
- Room width: 3.6 m (11.81 ft)