Font Loading Performance Calculator

Load impact from font file sizes.

Avg file size (KB)

Weights per family

Font families

Subset coverage (%)

Connection speed (Mbps)

Tab to move between fields

Total font payload (KB)

360

Total font files8

Subsetting savings (KB)0

Savings (%)0%

Est. load time (ms)528

FOIT risk score9.6/100

How to Use This Calculator

How the result changes with Avg file size (KB)

Avg file size (KB): Average size of each font file (WOFF2 typically 15–50 KB, TTF 50–200 KB).
Weights per family: Number of weights/styles loaded (e.g. Regular, Italic, Bold, Bold Italic = 4).
Font families: Number of different font families loaded (e.g. heading + body = 2).
Subset coverage (%): Percentage of glyphs kept. Latin-only subset is ~30–40%. 100% = no subsetting.
Connection speed (Mbps): User's download speed. 3G ≈ 1.5 Mbps, 4G ≈ 10 Mbps, broadband ≈ 50+ Mbps.

Total font payload (KB): Combined size of all font files after subsetting.
Total font files: Number of individual font files the browser must download.
Subsetting savings (KB): Kilobytes saved by subsetting compared to full character sets.
Savings (%): Percentage reduction from subsetting.
Est. load time (ms): Estimated total download time including connection overhead.
FOIT risk score: Risk of visible Flash of Invisible Text (0 = minimal, 100 = severe). Keep below 30.

Identify Input Parameters
4 parameters
Avg file size (KB) = 45, Weights per family = 4, Font families = 2, Subset coverage (%) = 100 = 5 input(s) provided
Calculate Total font payload
Total font payload = fullPayloadKb * (subsetPct / 100)
360 = 360
Calculate Total font files
Total font files
8 = 8
Calculate Subsetting savings
Subsetting savings = fullPayloadKb - subsetPayloadKb
0 = 0