Unit Converter — Convert Units Accurately & Understand Pitfalls
Unit conversion is routine in travel, cooking, engineering, and software. Small mistakes in units or rounding can produce significant errors. This guide explains unit families, precision rules, temperature conversions, presentation patterns, spreadsheet and API recipes, and practical tips to avoid common mistakes. The TimerHaven Unit Converter supports many families — length, weight, temperature, volume, area, speed, time, pressure, energy, power, data (SI & binary), fuel economy (L/100km ↔ mpg), angle and frequency — and includes UI helpers to make conversions safer.
Unit families & fundamentals
Units belong to families (length, mass, temperature, volume, time, area, energy, etc.). Always convert within the same family and pick authoritative conversion factors. The converter supports these families and provides sensible defaults and common units for each.
- Length: meter, kilometer, mile, foot, inch.
- Mass / weight: kilogram, gram, pound, ounce.
- Volume: liter, milliliter, cubic meter, gallons (US/Imperial), cups.
- Area: square meter, square foot, square yard, acre, hectare.
- Temperature: Celsius, Fahrenheit, Kelvin (affine transforms).
- Speed / Time / Pressure / Energy / Power: common engineering units included.
- Data sizes: SI (KB = 1,000) and binary (KiB = 1,024) modes — choose the right mode for context.
- Fuel economy: L/100km ↔ mpg (US/UK) — uses the correct formula (not a simple multiplier).
- Angle & Frequency: degree/radian and Hz/kHz/MHz.
For engineering-critical work, reference national standards (NIST, BIPM) for exact factors and unit definitions. The converter stores canonical factors centrally (recommended for automation).
Precision & rounding rules
Decide precision based on purpose. Overly aggressive rounding creates systematic bias; overly precise display can imply false accuracy.
Guidelines by context
- Everyday / shopping: 2 decimal places for currency and amounts that are presented to end-users.
- Cooking: round to sensible units (teaspoons, grams) and provide alternatives (metric & imperial).
- Engineering: display significant figures matching instrument precision (3–6+ decimals depending on tolerance).
- Analytics: store raw values at high precision and round only on presentation layers.
Always show units alongside numbers and consider showing the conversion factor or "as of" timestamp for dynamic rates (e.g., currency conversions). In the TimerHaven tool you can set display precision and see the raw value if rounding was applied.
Temperature — special-case conversions
Temperature conversions are affine: they require scaling and shifting. Converting an absolute temperature differs from converting temperature differences.
- Convert absolute values correctly:
- C → F: F = C × 9/5 + 32
- F → C: C = (F − 32) × 5/9
- C ↔ K: K = C + 273.15
- Converting a temperature change (Δ): convert with the scale only (multiply by 9/5 for ΔC → ΔF) — do not apply offsets.
Example mistake: "A change of 10°C is 18°F" is correct; but converting 10°C (absolute) to Fahrenheit requires adding 32 after scaling.
Common conversion recipes
- Use factor: 1 mile = 1.609344 kilometers.
- Example: 5 miles × 1.609344 = 8.04672 km → display 8.05 km for typical usage.
- Use factor: 1 square meter = 10.7639104 square feet (or 1 ft² = 0.09290304 m²).
- Example: 500 m² × 10.7639104 = 5,381.9552 ft² → display 5,382 ft² (0 decimals or as needed).
- US gallon → liter: 1 US gallon = 3.785411784 L; Imperial gallon = 4.54609 L.
- Example: 2 US gallons × 3.785411784 = 7.570823568 L → display 7.571 L (3 decimals for liquids in recipes).
- Use the proper formulas (not simple multipliers):
- mpg (US) → L/100km: L/100km = 235.214583 / mpg_US
- L/100km → mpg (US): mpg_US = 235.214583 / L/100km
- mpg (UK) uses constant ≈ 282.480936
- Example: 30 mpg (US) → L/100km = 235.214583 / 30 ≈ 7.8405 L/100km.
- Decide mode: SI uses 1 KB = 1,000 bytes; binary uses 1 KiB = 1,024 bytes.
- Example: 1,500,000 bytes → SI = 1.5 MB; Binary ≈ 1.4305 MiB.
Spreadsheet & script examples
Common formulas and script patterns help automate conversions at scale.
Spreadsheet example (Google Sheets / Excel)
Convert miles in A2 to kilometers: =ROUND(A2 * 1.609344, 2)
Square meters to square feet
Convert m² in A2 to ft²: =ROUND(A2 * 10.7639104, 0)
JavaScript snippet
function convertLength(val, fromFactor, toFactor) {
// where factors are expressed in meters per unit
return val * (fromFactor / toFactor);
}
// Example: meters->feet: metersFactor=1, footFactor=0.3048
// use consistent central factor table to avoid drift
Store canonical factors in one place and reuse them to avoid inconsistencies across sheets or code. For fuel economy and temperature use the prescribed formulas above — see the tool for L/100km ↔ mpg conversions and precision controls.
TimerHaven Unit Converter — features & advice
The online tool complements this guide. Key features to help avoid mistakes:
- Many families supported: length, weight, temperature, volume, area, speed, time, pressure, energy, power, data (SI & binary), fuel economy, angle, frequency.
- Data mode: switch between SI (1000) and binary (1024) when converting data sizes — only visible when Data is selected.
- Filter units: type to quickly find units like "square" or "ft".
- Swap: easily flip from/to units without retyping.
- Precision control: choose number of decimal places for display; raw value is available when rounding is applied.
- Copy result: copy formatted conversion to clipboard for quick pasting.
- Persistence & shortcuts: last-used settings persist in your browser; Ctrl+K focuses the value field.
- Sensible fallbacks: when a family-specific conversion isn't possible the tool falls back on canonical factors or shows an informative message.
Use the tool for quick checks but prefer authoritative references and stored canonical factors for production systems.
FAQ
Q: Why do imperial vs metric conversions sometimes look "off"?
A: Because rounding and display choices differ; also, some published factors (e.g., for gallons) vary by region (US vs UK). Always check which definition you're using.
Q: Which data mode should I use — SI or binary?
A: Use SI (KB = 1,000) for storage vendors and network contexts that advertise decimal units; use binary (KiB = 1,024) for low-level memory sizes and some OS/technical contexts. The tool lets you switch modes.
Q: How do I convert a temperature change vs an absolute temperature?
A: See the temperature section: temperature differences only use scaling (no offset).