Calculate running pace
Pick what you know — distance and time, distance and pace, or pace and time — and the third value drops out. Switch between km and miles.
How to compute pace
Two of distance, time, pace are enough to derive the third. Pick the mode for what you want to find.
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Pick mode
Find pace, find time, or find distance.
Inputs are treated as UTF-8 throughout the pipeline and validated client-side as you type — nothing dispatches until the value is well-formed.
modeinpututf-8client-sidevalidatedfind · textpace · setmode: pace
loaded · parsedclient-side - 02
Pick units
km or mi. Internally always normalized.
Each toggle re-computes through a memoised hook, so flipping options never resets your input and the UI stays snappy on large inputs.
unitoptionslivememoisedtogglesunit · memoisedkm · livemetric
options set · memoisedlive - 03
Enter values
Times accept h:m:s, m:s, or seconds-only.
Randomness — where used — comes from
crypto.getRandomValues, neverMath.random. Heavy work sits inuseMemo.inputcomputeinstantlocaldeterministict · instant50:00 · computed10 km / 50:00
computed · instantinstant - 04
Read all four
Pace/km, pace/mi, total time, and distance — all updated.
Copy writes through
navigator.clipboardand downloads use aBlob— zero network traffic. Same input plus same options always yield the same bytes.readcopydownloadzero-networkreproducibleok · copiedready · copied5:00 /km
shipped · ready to shipsuccess
Pro tips for everyday utilities
Reach for crypto.getRandomValues
Cryptographically random for IDs, tokens, salts. Math.random is for animation and games, not security.
Mock data with seeds
Faker-style libraries can be seeded so tests are reproducible. Embed the seed in the fixture file.
Reference cards beat memory
Cheatsheets for Vim, Git, Docker, Linux signals are faster than man pages when you’re mid-flow.
Browser APIs vary
Touch events, gamepads, and clipboard differ across vendors. Feature-detect before use.
Persist in the right place
localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data.
When pace matters
Race planning, training, splits, predictions.
Race day plan
Set realistic mile splits for a target time. Random values come from crypto.getRandomValues — cryptographically secure for tokens, salts, and session IDs. Math.random is deterministic enough for animations but predictable enough to be a security bug.
CSPRNG-backedWorkout intervals
Convert tempo paces between km and mi. Pair with hashids, ULID, or UUID v7 when you need both random and sortable — useful for primary keys, public-facing IDs, and event log ordering without a sequence column.
reproduciblePredict finish
Project a 10K pace to a half-marathon time. Output is deterministic given the same seed, so fixtures and tests stay reproducible across CI runs and contributor machines. Embed the seed in the fixture file for full replay.
snappyTreadmill math
Convert mph readings to min/mile splits. Heavy work runs through useMemo so the UI stays snappy on large inputs. Same input + same options yields identical bytes — the kind of stability snapshot tests rely on.
feature-detectedPacing strategy
Plan negative splits per kilometer. Storage tools persist to the right backend: localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data. Pick the right shelf and quota worries disappear.
deterministicTravel races
Switch units for international events. Browser feature detection: clipboard, fullscreen, gamepad, and Web Bluetooth APIs gracefully fall back when unavailable. No surprise white screens on Safari or older Firefox.
production-readyFrequently asked questions
Something missing?
Tell us what you need. We ship the top requests every two weeks.