Unit Conversion

Updated 17 Apr 2025

The unit query parameter (optional; default: empty) lets you restate an LCA metric’s functional unit (denominator) in a unit that matches your own reporting conventions.

Key rule Only the denominator changes; the numerator (e.g. “kg CO₂ eq”) always stays the same.

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1  Conversion workflow

1. Match chosen → API finds the “best” database record.
2. Identify functional unit → e.g. kg, m³, t·km…
3. Look‑up target unit → in the conversion map for that base unit.
4. Compute value → divide the original value by the conversion factor.
5. Return fields
   • metric.value – adjusted number
   • metric.unit – numerator / new denominator
   • conversion_info – human‑readable note on what happened

Example – kg → g

GET /api/metrics/search?item_name=cotton+t‑shirt&metric=Carbon+footprint&unit=g

Response (truncated):

{
  "metric": { "name": "Carbon footprint", "value": 0.0083, "unit": "kg CO2 eq / g" },
  "conversion_info": "Converted functional unit from kg to g (×10³ on denominator, value ÷1000)"
}

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2  Supported conversions

Below is the quick reference. Left column = base unit, bullets = accepted unit= values.

Base unit	Metric‑scale targets	Other‑system targets
kg	mg, g, t, μg, dag, hg, q, Mg	lb, oz, ton (US)
MJ	J, kJ, GJ, TJ, μJ, nJ, PJ	BTU, cal, kcal, kWh, hp·h
m³	cm³, dm³, L, mL, μL, hL, ML, cc	ft³, in³, yd³, gal (US), pt (US), fl oz (US), bbl (oil)
m²	cm², dm², mm², km², ha, a, μm²	ft², in², yd², acre, mi²
m	mm, cm, km, μm, nm, dm, Mm, Gm, pm	in, ft, yd, mi, nmi
s	ms, μs, ns, min, h, d, ps, ks, y, century, millennium	—
t·km	g·km, kg·km, mg·km, μg·km, kt·km, Mt·km	ton·mi, lb·mi, oz·mi, ton·yd
m³·km	cm³·km, L·km, dm³·km, ML·km, m³·m, m³·Mm	ft³·mi, gal·mi (US), in³·mi, yd³·mi, ft³·yd
pass·km	pass·m, pass·cm, pass·Mm, pass·Gm	pass·mi, pass·ft, pass·yd, pass·nmi

Need a unit that’s not here? Email support.

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3  Error & fallback behaviour

• Unsupported target → API keeps the original value/unit and sets conversion_info to explain.
• Incompatible base → same behaviour; no HTTP error is thrown.
• Precision → factors are applied with full float precision; rounding happens only in serialization.

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5  Quick tips

• If no target unit is set in the request, the base unit will be provided in the response.
• Specify only SI symbols (g, L, kWh…), case‑sensitive.
• For mass‑distance or volume‑distance units include the dot: t·km, m³·km.
• If the num_matches parameter is ≥1 (e.g.:num_matches=3), all the matched data units will be converted to the set target unit.