5-farads/5-farad

Treat a measurement that comes before a noun as an adjective: keep the unit singular and usually hyphenate the number + unit. Example: a 5-farad capacitor, not a 5-farads capacitor. When the measurement stands alone or follows a verb, use the plural as needed and don't hyphenate: The capacitor has 5 farads.

Quick answer

Before a noun: use a singular unit and hyphenate the compound (a 10-meter rope). After a verb or when the unit stands alone: use the plural as appropriate and don't hyphenate (The rope is 10 meters long).

Adjectival (before noun): singular unit + hyphen - a 12-volt battery.
Nominal/after verb: plural unit, no hyphen - The battery is 12 volts.
Symbols: normally use a space (5 kg). Some technical guides accept a hyphenated symbol (5-kg) for adjectival use - be consistent.

Core rule (short and exact)

When a number + unit modifies a noun, it forms a compound adjective. English adjectives don't take a plural -s, so the unit stays singular. When the measurement functions as a noun (after a verb or alone), pluralize the unit as appropriate.

Before noun (adjective): singular unit, usually hyphenated - a 3-mile race, a 5-farad capacitor.
After verb/standalone (noun): plural as appropriate, no hyphen - The race is 3 miles; the capacitor has 5 farads.

Wrong: a 5-farads capacitor
Right: a 5-farad capacitor
Wrong: The capacitor has 1-farad.
Right: The capacitor has 1 farad.

Hyphens and compound modifiers

Hyphenate a number + unit when the pair acts together to modify a noun. The hyphen signals that the words form a single adjective. Do not hyphenate when the measurement follows the noun or when you use a symbol separated by a space.

Adjective before noun: hyphenate - a 20-year-old intern, a 5-kW generator.
After noun or with symbol: no hyphen - The generator is 5 kW; she is 20 years old.
Hyphens reduce misreading (compare a small-business owner vs a small business owner).

Wrong: a 3-miles run
Right: a 3-mile run
Wrong: Install a 15-amps fuse.
Right: Install a 15-amp fuse. (The fuse is 15 amps.)

Spacing, symbols, and abbreviations

Unit symbols normally have a space after the number (5 kg, 100 m). Spelled-out units used adjectivally are usually hyphenated (a 5-kilogram box). In technical documents you may see hyphenated symbols (a 5-kg package); choose one convention and use it consistently.

Standalone with symbol: 5 kg, 100 m.
Adjectival spelled-out: a 5-kilogram package (hyphen).
Adjectival symbol (technical): a 5-kg package (accepted in specs).

Wrong: 5-kgs of cement
Right: 5 kg of cement
Wrong: a 2-lb chicken (in casual, non-technical copy)
Right: a 2-pound chicken (spelled-out) / a 2-lb chicken (acceptable on packaging)

How to fix your sentence now (fast checklist + rewrites)

Checklist: 1) Is the measurement before a noun? → make the unit singular and hyphenate. 2) Is it after a verb or standing alone? → pluralize the unit if >1 and don't hyphenate. 3) Using symbols? Use a space (5 kg) or, in technical contexts, a consistent hyphenated symbol.

If you're unsure, move the measurement after the noun or rewrite with "X units of Y" - both options are clear and safe.

Before noun: singular + hyphen - a 10-foot ladder.
After noun/standalone: plural as needed, no hyphen - The ladder is 10 feet long.
When in doubt: rewrite to put the number after the noun or use "X units of Y."

Wrong: We ordered 20-kilos of sugar for the event.
Rewrite: We ordered 20 kg of sugar for the event.
Wrong: Install 15-amps fuse in the panel.
Rewrite: Install a 15-amp fuse in the panel.
Wrong: Bring 2-litters water to lab class.
Rewrite: Bring 2 liters of water to lab class.

Try your own sentence

Test the whole sentence rather than the isolated phrase; context usually shows whether the unit should be adjectival or nominal.

Practical examples: work, school, and casual

Quick wrong/right pairs to copy when editing specs, lab reports, or messages.

Work - Wrong: The spec lists 12-volts batteries for the device.Work -
Right: The spec lists 12-volt batteries for the device.
Work - Wrong: Fit a 100-meters cable to the router.Work -
Right: Fit a 100-meter cable to the router.
School - Wrong: Provide 250-milliliters samples to each group.School -
Right: Provide 250-milliliter samples to each group.
School - Wrong: The solution needs 0.5-liters of solvent.School -
Right: The solution needs 0.5 L of solvent. / The solution needs 0.5 liters of solvent.
Casual - Wrong: I bought 2-kilos of apples at the market.Casual -
Right: I bought 2 kg of apples at the market. / I bought 2 kilos of apples.
Casual - Wrong: He's a 6-feet tall guy.Casual -
Right: He's 6 feet tall. / a 6-foot-tall man

Real usage and style guide notes

SI guidance: use singular unit names in adjectival form and put a space between number and unit symbol (5 kg). Editorial and technical styles vary: some prefer hyphenated symbols (5-kV) in specs; scientific texts usually use a space (5 kV). The key is consistency within a document.

Scientific work: follow SI recommendations (space between number and symbol, consistent symbols).
Engineering/tech: hyphenated symbols are common in specs - follow your organization's guide.
Journalism: follow house style; when in doubt, pick the clearer form.

Usage: a 5-kV transformer (engineering report) / The transformer is 5 kV (spec sheet).
Usage: 20 °C or 20°C depending on your guide - be consistent about spacing.

Memory tricks and quick heuristics

Three short heuristics will catch most errors: modifier = single unit; standalone/after noun = plural as needed; symbols use a space (unless your technical style says otherwise).

Modifier → single unit: a 7-inch screen.
Standalone → plural if needed: The screen measures 7 inches.
Symbol spacing: 5 kg; if hyphenating a symbol for specs, use it consistently (a 5-kg chart).

Similar mistakes and troubleshooting checklist

Common slips include adding -s to unit symbols (kgs), using plural adjectives with plural nouns (a 6-feet men), and misplaced hyphens that create confusing compounds. Use the checklist below to fix sentences quickly.

Common confusions: avoid adding -s to unit symbols (write 5 kg, not 5 kgs) and don't pluralize "percent" in numeric expressions (50 percent).
Checklist: 1) Is number+unit before a noun? → singular + hyphen. 2) Is it after the noun or standalone? → plural if >1, no hyphen. 3) Symbol in use? → space and consistency.

Wrong: 5-kgs of cement
Right: 5 kg of cement
Wrong: a 6-feet tall athlete
Right: a 6-foot-tall athlete

FAQ

Should I write 5-farads or 5 farads?

Use 5-farad when the phrase modifies a noun (a 5-farad capacitor). Use 5 farads when the unit stands alone or follows a verb (The capacitor has 5 farads).

Do you write 5-kg or 5 kg?

For standalone measurements use a space: 5 kg. For adjectival use, spell it out and hyphenate (a 5-kilogram package) or, in technical contexts, a hyphenated symbol may be acceptable (a 5-kg package). Be consistent with your style guide.

Is it wrong to write "10-meters long"?

Yes. When the measurement follows the noun, write "10 meters long." Use "a 10-meter rope" when the measurement modifies the noun before it.

What's the safest rewrite if I'm unsure?

Move the measurement after the noun or use the symbol with a space. Example: change "a 20-meters pipe" to "a 20-meter pipe" or "The pipe is 20 meters long."

Can I pluralize percent (50 percents)?

No. Use "percent" with numbers: 50 percent. Don't add -s to "percent" in numeric expressions.

Want a quick check for your sentence?

Paste your sentence into a grammar or style checker that flags unit usage and hyphenation, or apply the checklist above: move the measurement after the noun or make the unit singular and hyphenate when it modifies a noun.